But pimps find ways around the filters, said BSO’s Weller, who also works as part of the FBI’s Minor Vice Task Force.

They learn to avoid the words for which Backpage.com screens, Weller said. Both cops and customers now assume that the girls pictured in websites are younger than advertised. If the real picture is too obvious, no problem: Pimps will substitute a woman with more seasoning.

In a letter to Village Voice, the National Association of Attorneys General called the screening efforts window dressing.

The filters failed to raise a red flag when a Miami couple posted pictures of a 15-year-old girl on the website last May.

The girl told police a 22-year-old woman from her neighborhood approached her in late March and “told her that she would post [her] on the website ‘backpage’ and that no one would find out,” according to a criminal complaint.

She wore lingerie in the ad.

She was told never to undress until after her customer did so first, insist on being paid up-front, and always ask whether the client was a cop. She was to charge $70 for 15 minutes of work, $100 for 30 minutes and $170 for a full hour.

The 15-year-old earned her first payment her very first day, $100 that she was allowed to keep. On her second work day, she generated $175 but only got to keep $25.

Her stint as a prostitute was short-lived. On May 4, the girl’s mother called the Hialeah Police Department, which returned the teen to her family.

Why can’t technology detect that she didn’t belong on a site like Backpage.com? That’s a question being asked by researchers, including Mark Latonero, research director at the Annenberg Center on Communication Leadership and Policy at the University of Southern California.

Latonero’s human trafficking online report, published last year, says the Craigslist shutdown, followed by the migration to Backpage, suggest that truly ending human trafficking is more complicated than shutting down one website. The entire ecosystem — from the recruitment to the grooming and the selling, almost all done via the Internet — must be addressed.

But his work also takes Backpage.com and other members of the online community to task for not doing enough to protect children from becoming victims of human trafficking.

“The private sector capitalizes on the online visibility of Internet users by routinely collecting data on consumer behaviors for targeted marketing and advertising strategies,” he wrote. “Yet efforts to harness data and technological tools to address social problems lag behind.”