Chicago- Cook County Sheriff Tom Dart announced today that his office has sued Craigslist and has asked a federal judge to ban the Internet company from posting its “erotic services” section, which the sheriff said is a clearing house for prostitution.

Dart also asked the judge to force the online classifieds company to reimburse the sheriff’s department for the approximately $100,000 it has spent pursuing its Craigslist investigation over the past year.

“Craigslist is the single largest source of prostitution in the nation,” Dart said.

He added later, “I could make arrests off Craigslist 24 hours a day, but to what end?” By filing the suit, he said, “I’m trying to go up the ladder.”

Dart said he had been working with Craigslist representatives for months, sending letters requesting them to take down or provide greater self-policing of their “erotic services” section, but his pleas have been met with no response.

The sheriff said he believes the company has been unresponsive because the “erotic services” section generates a large portion of the company’s $80 million annual revenue.

“They have crafted their site to accommodate people,” the sheriff said. “None of the ads require any imagination. There’s no mystery at all. We all know what’s going on here.”

A 19-year-old woman, who was not identified, appeared at a press conference with the sheriff and said she was drawn into prostitution after she applied for modeling work through a different section of Craigslist.

“It started out as a photo shoot. That’s not enough — they don’t want you to do just a photo shoot,” she said.

The woman said that undercover Cook County sheriff’s police recently met with her at a hotel room in the south suburbs and she was subsequently arrested for prostitution. But she said authorities told her they could tell she had been a victim herself.

“I thank God that the officers picked me up. This is something that will go on for life,” she said.

The woman said that even after her arrest, her photos are still being posted on the “erotic services” section.

“Even after you get ‘clean,'” she said, “they still have your photos and they can post them anywhere.”

The woman spoke calmly but her voice and hands shook at times.

Among recent prostitution-related ads that the sheriff’s office has monitored were one advertising “15 min $50 roses … 1 hour $150 roses,” and another saying a “busty blonde pregnant beauty” was available, according to the sheriff’s office.

Over the years, Dart’s office has made dozens of arrests of people accused of using Craigslist for prostitution.

Last June, Cook County sheriff’s police arrested 76 men and women on prostitution-related charges in a sting involving Craigslist. Undercover officers posed as customers who made dates with women featured in “erotic services” ads on the site. Once an offer of sex for money was made, the woman was taken into custody, officials said.

In December of 2007, four Chicago-area men were charged with using Craigslist to run a prostitution ring that employed girls as young as 15. Dubbed Operation Quiet Money, the three-month investigation monitored advertisements on the Web site.

In January of that year, the sheriff’s office estimated that it had already busted nearly 75 women accused of selling sex on Craigslist in the last 18 months.

Craigslist today denied that it knowingly facilitates prostitution. In an e-mail message to The Associated Press, spokeswoman Susan Best said the company has taken several steps to prevent the illegal use the site, works willingly with law enforcement and pulls inappropriate ads.