"He's a con artist, a monster and a manipulator," another victim testified at his sentencing. "I was brainwashed into believing that having sex with men for money was normal, an everyday thing."
An FBI operation shut Strom's gang down last year, and in September he was sentenced to 40 years in prison. Four of his associates were also convicted.
But FBI cybercrimes supervisor Jack Bennett says Strom's tactics are becoming more common. Part of the problem, he says, is that minors will accept friend requests from strangers just to appear to be popular. Photos, personal information, and friend lists are then out in the open.
Pimps "start looking for the cracks where they can fill the holes, whether it be a father figure or a boyfriend," Bennett says.
Some are even more direct.
"Lisa," a 21-year-old who was a sex worker on and off for three years before escaping in mid-2012, gets daily messages on social networking sites from traffickers trying to reel her back in. Many don't even hide their intentions.
"If it's a 'P' beside their name, that stands for pimp," Lisa says. On any given day, she gets a steady stream of messages from unfamiliar men whose last names are just "P."
'Old tricks with new tools'
Powell, the advocate who runs Fair Girls, says she's seen girls recruited from almost every social network that exists. Facebook and Tagged are two of the most common, she says, but even more limited sites like Twitter and Instagram get used for solicitation. The FBI's case against Strom cites DateHookup and MySpace, in addition to Facebook, as sites his gang targeted.
In a recent Seattle case involving multiple juveniles, Facebook was used to recruit one of the victims. The two defendants were charged in Pierce County, Wash., in November.
"What you're really seeing here with Facebook, and other social networking sites, is old tricks with new tools," says Pierce County prosecutor Mark Lindquist.
The Polaris Project, which runs a sex-trafficking help hotline, works with tech companies to educate them on how their technology is being used to facilitate trafficking, and how they can help stop it.
"They're most interested in understanding exactly how the criminal networks are operating, and they want to know the modus operandi of the traffickers," says Bradley Myles, executive director of Polaris.
Facebook reacts swiftly to reports of illicit activity and quickly takes down questionable content when it's flagged, according to Myles and other advocates.
The company says it takes human trafficking very seriously.
"While this behavior is not common on Facebook, we have implemented robust protections to identify and counter this activity," a company representative told CNNMoney in a written statement. "We have zero tolerance for this material and are extremely aggressive in preventing and removing exploitative content. We've built complex technical systems that either block the creation of this content, or flag it for review by our team of investigations professionals."
But algorithms can't catch everything, and pimps are skillful social engineers.
During down time, Nina's pimp browsed through her Facebook friends, sending friendship requests using her profile and messaging women he thought "looked the part."
Strom used similar tactics, relying on women he controlled to reach out to new prospects. He also sent hundreds of messages himself to teenagers, with pitches like: "I work with girls that dance nude do partys dates one on ones and more does any of that interest you."
Calvin Winbush, who calls himself "Good Game," ran a prostitution business out of Ohio. He was sentenced in August to 14 years in prison for trafficking minors across state lines for prostitution. Winbush described himself as an "international player" on his Facebook page, and recruited heavily with messages like: "Call me soon as u get this love so we can chop it up and get better acquainted..."