Just 13.

That's the average age UNICEF reports that girls enter the commercial sex trade in the U.S.

And while many Americans might think of sex trafficking as an international problem, it often starts in the United States. Prosecutor Lindsey Roberson has seen it happen.

One of her first cases involved a 17-year-old girl who met a guy at a downtown club. He wooed her, and then "took her out of town on a trip, and let her know what she would have to do to pay her way," Roberson said.

"She had no ID, no cell phone; no way to contact her mother. And the guy ended up advertising her for sex on Backpage.com and trafficking her all the way out to California and back to Virginia."

The difference between sex trafficking and freelance prostitution is who has the control and who is keeping the money, said Roberson, an assistant district attorney in New Hanover County. If a girl or a woman is being forced or coerced by a pimp to perform sex acts without monetary gain, that's trafficking.

The North Carolina Coalition to Combat Human Trafficking ranks the state among the top 10 states for the problem. North Carolina's three major highways connect much of the East Coast, and the state has a large transient military and farmworker population, and international seaports in the Cape Fear region.

In May, Roberson helped start a deferred prosecution pilot program for first-time offenders with prostitution charges, partnering with a local rape crisis center.

As a Christian, Roberson is also on the board of a new faith-based effort called the Centre of Redemption, which is scheduled to open in December to help pregnant teens and teen moms who are also trafficking victims.

Law enforcement is increasingly teaming up with faith groups to combat sex trafficking around the country. Some are calling the faith-based push against human trafficking the newest "Christian abolitionist movement."

In California, an Underground Church Network has formed to help U.S. trafficking victims. The Evangelical Lutheran Church in America has developed a human trafficking curriculum. And the National Association of Evangelicals' humanitarian arm, World Relief, told CNN in February that its North Carolina offices had seen a 700 percent rise in reports of human trafficking last year.

Religious groups have also rallied against Backpage.com, which is owned by Village Voice Media, which they say is a haven for pimps and traffickers.

The issue drew the attention of President Obama at former President Bill Clinton's Clinton Global Initiative on Tuesday, where Obama said the estimated 20 million victims of human trafficking would become a major focus of his Office of Faith-based and Neighborhood Partnerships.

"Like that Good Samaritan on the road to Jericho, we can't just pass by, indifferent," Obama said. "We've got to be moved by compassion. We've got to bind up the wounds."

In Wilmington, The Centre of Redemption, founded by former local banker MaLisa Johnson, will be funded by grants and local churches as the first boarding school of its kind in the state. The Centre will start small, accepting two teens and their children and will expand, Johnson said.

"Traffickers will actually purposefully impregnate a girl to control her and will sometimes sell the child on the black market," Johnson said.

Girls will be referred to the center from other parts of the country where they left the sex trade because the center can't admit local teens for safety reasons, Johnson said.

"You don't want to ever house a girl where she was trafficked because she might see her pimp or be tempted to go back into the life or even see a previous buyer," she added. The home's location also will be kept secret for the girls' protection.

The Centre will contract with local faith-based educators and pregnancy centers for trauma counseling and motherhood options. Female volunteers are being trained from 14 local churches to teach life skills.

As the girls age, Johnson plans to open a home for adult women to offer continuous care with the hope of keeping them on a healing path into adulthood.

The Centre is working with local law enforcement, setting up a toll free human trafficking hotline and will collect clothing and personal items for women who are rescued. It also plans to start a sex trafficking community outreach campaign in local hotels and motels to help business owners spot and report it to police.

Johnson, an evangelical, began the effort to organize the center after being laid off last year. Her boyfriend was donating to a faith-based organization that helped sex trafficking victims, and she became curious about the problem.

"I couldn't believe that something like that could be happening here," Johnson said. "But once I started researching it I became obsessed, and I felt like I should do this. God has just continued to put the right people in my life to make it happen."

Amanda Greene is the editor of WilmingtonFAVS.com in Wilmington, N.C.