ASHLAND, Ore. » She ran away from her group home in Medford, Ore., and spent weeks sleeping in parks and under bridges. Finally, Nicole Clark, 14 years old, grew so desperate that she accepted a young man's offer of a place to stay. The price would come later.

They had sex, and he soon became her boyfriend. Then one day he threatened to kick her out if she did not have sex with several of his friends in exchange for money.

She agreed, fearing she had no choice. “;Where was I going to go?”; said Nicole, now 17 and living here, just down the Interstate from Medford. That first exchange of money for sex led to a downward spiral of prostitution that lasted for 14 months, until she escaped last year from a pimp who she said often locked her in his garage apartment for months.

“;I didn't know the town, and the police would just send me back to the group home,”; Nicole said, explaining why she did not cut off the relationship once her first boyfriend became a pimp and why she did not flee prostitution when she had the chance. “;I'd also fallen for the guy. I felt trapped in a way I can't really explain.”;

Most of the estimated 1.6 million children who run away each year return home within a week. But for those who do not, the desperate struggle to survive often means selling their bodies.

Nearly a third of the children who flee or are kicked out of their homes each year engage in sex for food, drugs or a place to stay, according to a variety of studies published in academic and public health journals. But this kind of dangerous barter system can quickly escalate into more formalized prostitution, when money changes hands. And then, child welfare workers and police officials say, it becomes extremely difficult to help runaways escape the streets. Many become more entangled in abusive relationships, and the law begins to view them more as teenage criminals than underage victims.

Estimates of how many children are involved in prostitution vary wildly—ranging from thousands to tens of thousands. More solid numbers do not exist, in part because the Department of Justice has yet to study the matter even though Congress authorized it to do so in 2005 as part of a nationwide study of the illegal commercial sex industry.

But many child welfare advocates and officials in government and law enforcement say that while the data is scarce, they believe that the problem of prostituted children has grown, especially as the Internet has made finding clients easier.

“;It's definitely worsening,”; said Sgt. Kelley O'Connell, a detective who until this year ran the Boston Police Department's human-trafficking unit, echoing a sentiment conveyed in interviews with law enforcement officials from more than two dozen cities. “;Gangs used to sell drugs,”; she said. “;Now many of them have shifted to selling girls because it's just as lucrative but far less risky.”;

Atlanta, which is one of the only cities where local officials have tried to keep data on the problem, has seen the number of teenage prostitutes working in the city grow to 334 in February from 251 in August 2007.

The barriers to rescuing these children are steep: state cuts to mental heath services, child welfare agencies incapable of preventing them from running away, a dearth of residential programs where the children can receive counseling.

After years of abuse, trauma and neglect, the children also tend to trust no one. The longer they are on the streets, experts say, the more likely they are to become involved in crime and uncooperative with the authorities.

“;These kids enter prostitution and they literally disappear,”; said Bradley Myles, deputy director of the Polaris Project, a nonprofit organization based in Washington that directly serves children involved in prostitution and other trafficking victims. “;And in those rare moments that they reappear, it's in these revolving-door situations where they're handled by people who have no idea or training in how to help them. So the kids end up right back on the street.”;

THE FLIP INTERVIEW

That revolving door is what an FBI agent, Dan Garrabrant, desperately hoped to stop in Interview Room One at the Atlantic City Police Department on Sept. 5, 2006.

Conducting what the police call a “;flip”; interview, Garrabrant was trying every tactic he knew to persuade a petite 16-year-old girl named Roxanne L. from Queens, N.Y., to stop being a prostitute and to inform, or flip, on her pimp.

Sending the girl home was not the answer. Home was where her mentally ill, crack-addicted mother lived. Home was where the problems had started.

But Garrabrant also knew that she would flee if he sent her to a youth shelter. And with her would go his best chance at prosecuting the real criminal, her pimp.

A social worker for six years before joining the FBI almost two decades ago, Garrabrant has been honored by anti-trafficking experts, prosecutors and the police as one of the best flip interviewers in the country.

On this day, however, he was getting nowhere, according to a recording of the interview and his notes.

While Roxanne had all the signs of being controlled by a pimp—a tattoo with initials on her neck, a rehearsed script about how she was new to the work—she adamantly denied working for anyone.

Garrabrant had only an hour before the local police would take Roxanne to a shelter. Trying to ease the mood, he started by asking her why she had run away from home. She told him she had been raped by a relative when she was 12 years old. At 14, she left home because her mother's boyfriend had become abusive.

Soon, running out of time, he zeroed in.

“;What's the worst part about working the streets?”; he asked.

“;Honestly,”; Roxanne said, giving him a cold stare, “;having to look at the tricks and tell if they are cops or not.”;

“;So a pimp never approached you and tried to turn you out?”; Garrabrant asked.

“;Yeah, they tried, but I ran,”; she said, maintaining that she was “;renegading,”; or working without a pimp.

Garrabrant's task was to get Roxanne to consider leaving her pimp without forcing her to admit she had one. He needed to push hard enough to break her from her rehearsed script, without descending into a frustrating game of wits, a contest in liar's poker. And he had to do all this at exactly the wrong time and place—at the police station after an arrest for solicitation, when the girl felt most panicked and most angry about being treated like a criminal.

“;Look, I want to help you,”; he said, after several failed attempts to get her to acknowledge her pimp. He told her that he might be able to enter her into a residential program in California that offered counseling and classes to girls leaving prostitution.

“;Yeah, I know,”; she said, as she looked down and pensively picked at her nails.

“;Give me some time,”; Garrabrant pleaded as he handed her a card and asked her to keep it handy. With no time left, he released Roxanne back to the local police, who took her to the youth shelter.

Four hours later, she disappeared. Seventeen days after that, according to the FBI she was found stabbed to death by the pimp she had so adamantly denied existed.

In one of her pockets she had Garrabrant's card.

“;Two days, that's all I needed to get her to stay away from her pimp and I think things would've ended up differently,”; said Garrabrant, shaking his head in frustration. “;I still don't understand how these guys loop these girls in so far.”;

A DANGEROUS DEPENDENCY

A runaway's relationship with a pimp does not occur by accident. It takes work.

After using court records to compile a database of over a hundred convicted pimps and where each is incarcerated, The New York Times began interviews more than two years ago. In interviews by phone and in letters, more than two dozen convicted and still incarcerated pimps described the complicated roles they played as father figure, landlord, boss and boyfriend to the girls who worked for them. They said they went after girls with low self-esteem, prior sexual experience and a lack of options.

“;With the young girls, you promise them heaven, they'll follow you to hell,”; said Harvey Washington, a pimp who began serving a four-year sentence in Arizona in 2005 for pandering a 17-year-old and three adult prostitutes. “;It all depends on her being so love-drunk off of me that she will do anything for me.”;

While most of the pimps said they prefer adult women because teenage runaways involve more legal risks, they added that juveniles fetch higher prices from clients and are far easier to manipulate.

Virtually all the juveniles who become involved in prostitution are runaways and become pimp-controlled, according to law enforcement officials and social workers. Built of desperation and fear, the bonds they form with their pimps are difficult to break. Some girls continue working for pimps even after the pimps are incarcerated.

“;The problem is that there is no methadone for a bad relationship,”; said Rachel Lloyd, a former child prostitute and the director of Girls Educational and Mentoring Services, a program in New York that helps girls escape and stay away from prostitution.

The pimps view themselves as talent mangers, not exploiters.

“;My job is to make sure she has what she needs, personal hygiene, get her nails done, take her to buy an outfit, take her out to eat, make her feel wanted,”; said another pimp, Antoin Thurman, who was sentenced in 2006 to three years for pandering and related charges in Buckeye, Ariz. “;But I keep the money.”;

Wayne Banks Jr., a pimp serving at least 40 years in Hazelton, W.Va., for the sex trafficking of a minor and related charges, wrote that the girls have to be convinced that the pimp is best equipped to handle their clients and finances.

“;Seems more despicable to me to give something so valuable away as opposed to selling it,”; he wrote, describing his pitch to persuade girls that prostitution was a smart business decision.

When recruiting, some pimps said they prowled homeless shelters, bus stations and shopping malls or posed in newspaper advertisements as photographers and talent scouts. Others said they worked Internet chat rooms and phone-sex lines.

“;I'll look for a younger female with a backpack,”; said Thurman, describing how he used to drive near schools after hours. “;I'm thinking she's leaving home, she's leaving for a reason, she had a fight with her parents or she just wants to leave home.”;

Banks wrote that he preferred using “;finders' fees”;: $100 to anyone who sent a prospect his way. His only condition was that the girl had to be told up front that he was a pimp.

Runaways are especially attractive recruits because most are already engaging in survival sex for a place to stay, said Evelyn Diaz, who is serving a nine-year sentence in a federal prison in Connecticut for three counts of sex trafficking of minors.

“;Some become very loyal to you since you take them under your wing,”; she wrote.

Controlling girls through beatings or threats was common, but coercion was not an effective basis for a lasting relationship, most pimps emphasized.

“;Everything about the game is by choice, not by force,”; said Bryant Bell, who is serving a four-and-a-half-year sentence in Georgia after pleading guilty in 2002 to helping run a prostitution ring that involved girls as young as 10 years old.

For those girls not already engaged in survival sex, the grooming process was gradual and calculated. At first, the sex is consensual. Before long, the girl is asked to turn occasional tricks to help pay bills.

“;I might start by asking her to help me by sleeping with a friend,”; Washington said in a telephone interview. “;Then I push her from there.”;

A BETTER SYSTEM

Ten years ago, the Dallas Police Department found an average of fewer than 10 minors working as prostitutes every year, along with one pimp working with them. In 2007, the department found 119 girls involved in prostitution and arrested 44 pimps.

The city's child prostitution problem has grown over time. But the bigger reason for the change is how the department handles the cases, using a special unit and some unusual techniques.

Previously, said Sgt. Byron A. Fassett, who leads the department's effort, girls working as prostitutes were handled as perpetrators rather than sexual assault victims. If a 45-year-old man had sex with a 14-year-old girl and no money changed hands, she was likely to get counseling and he was likely to get jail time for statutory rape, Fassett said. If the same man left $80 on the table after having sex with her, she would probably be locked up for prostitution and he would probably go home with a fine as a john.

The department's flip interviews almost always failed, and even if they worked, there was no place to put the girls to receive treatment. Officers resisted investigating what they viewed as a nuisance, not a crime. Prosecutors regularly refused the cases against pimps because the girls made for shaky witnesses and unsympathetic plaintiffs.

Frustrated with this system, Fassett started combing through old case files, looking for patterns. One stuck out: 80 percent of the prostituted children the department had handled had run away from home at least four or more times a year.

“;It dawned on me, if you want to effectively deal with teen prostitutes, you need to look for repeat runaways,”; he said.

In 2005, Fassett created the “;High Risk Victim”; unit in the Dallas Police Department, which flags any juvenile in the city who runs away from home four or more times in a given year. About 200 juveniles per year fit that description. If one of those children is picked up by the police anywhere in the country, the child is directed back to Fassett's unit, which immediately begins investigating the juvenile's background.

The unit's strength is timing. If the girls are arrested for prostitution, they are at their least cooperative. So the unit instead targets them for such minor offenses as truancy or picks them up as high-risk victims, speaking to them when their guard is down. Only later, as trust builds, do officers and social workers move into discussions of prostitution.

Repeat runaways are not put in juvenile detention but in a special city shelter for up to a month, receiving counseling.

Three quarters of the girls who get treatment do not return to prostitution.

The results of the Dallas system are clear: In the past five years, the Dallas County district attorney's office has on average indicted and convicted or won guilty pleas from over 90 percent of the pimps arrested. In virtually all of those cases, the children involved in the prostitution testified against their pimps, according to the prosecutor's office. Over half of those convictions started as cases involving girls who were picked up by the police not for prostitution but simply as repeat runaways.

In 2007, Congress nearly approved a proposal to spend more than $55 million for cities to create pilot programs across the country modeled on the Dallas system. But after a dispute with President George W. Bush over the larger federal budget, the plan was dropped and Congress never appropriated the money.