MILWAUKEE -- Law enforcement officers are concerned about an increase in prostitution on Craigslist, the popular classified advertising Web site.

Court documents unsealed in Milwaukee this week said that a 15-year-old girl who ran away from her home in Onalaska last fall posted an ad and photo on Craigslist. She told detectives she sold sex acts to 10 men in Milwaukee in 14 days, earning $1,500.

Milwaukee police Capt. Timothy Burkee said that it seems the more people they arrest for selling sex on Craigslist, the more people post prostitution ads.

The San Francisco-based Craigslist doesn't allow ads promoting illegal activity, but some prosecutors say the operators haven't done enough to keep the ads off the Web site.