At age 17, Tiffany already had four cellphones. In three, she kept a phone number for a man she called “Shadow.”

In the fall of 2010, Shadow — whose real name is Miguel Pierre Morancy — called Tiffany 2,687 times on two of the phones, court documents say, and a “ridiculously high number of times” on the others.

Morancy, federal prosecutors say, was her pimp.

Federal prosecutors say Morancy peddled underage girls, including Tiffany, to Tampa Bay area customers by placing graphic advertisements in the adult-themed section of a website called Backpage.com.

The website, owned by Village Voice Media, is popping up in court papers and arrest affidavits across the country as a bulletin board for men to traffic children, including some recent cases involving Florida foster children in the Homestead and Jacksonville areas.

The free online classified service Craigslist used to be the king of classified advertising for sexual services. Then, under intense criticism from lawmakers and advocacy groups, Craigslist shut down the ads in 2010.

Many of them found their way to Backpage.com, where the debate reignited.

Advocacy groups have demanded the adult sections be shut down immediately. Legal counsel for Backpage.com say they work hard with authorities to ferret out ads involving the underage and that shutting down the service wouldn’t stop underage prostitution.

Somewhere in between those two camps are a handful of researchers who want to see a sweeping approach to stamping out underage prostitution, not just on Backpage.com, but on multiple websites, in chat rooms and even Facebook.

In Morancy’s case, he pleaded guilty this year to one count of “affecting interstate commerce” with a 14-year-old girl engaged in commercial sex acts. The rest of the counts were dropped. He will be sentenced this fall.

But how many girls like Tiffany are on Backpage.com? That’s unclear.

What’s certain is that the world of underage prostitution has moved off the street and onto the Internet, where it’s a few links away.

Anyone can click through the disclaimers and land in the adult section for a specific city, tucked off to the right side, sandwiched between dating and services, such as landscaping and housecleaning. It includes sections labeled “escorts” and “body rubs.”

Every person pictured says she’s older than 18, even if a youthful face suggests otherwise.

Ernest Allen, who has semi-retired as head of the National Center for Missing and Exploited Children, said Backpage is unique among websites that market sex in that husbands, fathers and business leaders can visit the site without arousing suspicion: “You can apply for a job, sell your car or buy a toaster,” he said. “And you can also buy a kid.”

Among those pressuring Backpage to discontinue the advertisements or demand proof of age of those featured in the classifieds are top prosecutors in 46 states, 19 U.S. senators, the U.S. Conference of Mayors and the New York City Council.

The legal counsel for Village Voice Media, which owns a number of well-respected alternative newspapers, including Miami New Times, says the company cooperates with law enforcement, screens adult ads three times for signs of underage prostitution and insists that, if they did shut down the adult ads, the activity would only move to another website.