An ad on the Internet classified website Craigslist under the “casual encounters” category leaves little to the imagination.

For a man willing to pay $30, a woman who calls herself “sexy and attractive,” among other descriptors, will be willing to meet at a location north of the metro Atlanta perimeter.

“My man will be attending,” the ad reads in part. “We are ready. You must pay the $30 for us.”

Critics say such ads obviously promote prostitution. Hall County law enforcement has confirmed they’ve made stings using Craigslist. And a new study commissioned by a Georgia advocacy group claims Craigslist is the most popular place on the Web to sell sex.

“On the Internet, Craigslist is really the elephant in the room,” said Kaffie McCullough, campaign director for A Future Not A Past, a project that targets underage prostitution. “A john (customer) is three times as likely to go to Craigslist as any of the other sites.”

McCullough said the group estimates that in years past, the Internet accounted for 40 percent of sex trafficking of girls.

“Now it’s 70 percent, and the vast majority is occurring on Craigslist,” she said.

A spokeswoman for Craigslist, after briefly responding to an e-mailed request from The Times for comment, did not respond to the group’s allegations. The company has routinely declined to comment for news articles about prostitution on the Web.

On the web log of Craigslist CEO Jim Buckmaster, the company noted it is “operating in full compliance with all applicable laws” and has “earned a reputation for being unusually responsive to requests from law enforcement.”

The company said it has also adopted strict screening measures for its ads in its adult services section, which was formally known as its “erotic services” section until that name was eliminated last year.

Indeed, last weekend two of the 58 Metro Atlanta area ads for “women for men” casual encounters had been flagged for removal.

But critics say the company’s work with law enforcement is not enough.

“There was a time when I believed that,” McCullough said. “But it’s increasing so much.”

A study conducted by The Schapiro Group estimated that Craigslist ads attract 7,200 men in Georgia each month looking to pay for sex with adolescent girls.

For the study, the group created fake ads and a phone number and fielded calls from would-be johns in what it called a “reverse survey.”

“It’s my belief from all the research I’ve conducted that there is no real situation under which Craigslist could, or anyone else could, police the ads that are on the site to ensure no child is prostituted on their website,” said the study’s lead researcher, Alex Trouteaud.

Officers with the Hall County Multi-Agency Narcotics Squad, which investigates all vice-related crimes, have more than once used Craigslist to make prostitution cases.

According to court documents, two years ago a pimp and a prostitute met an undercover officer at a Friendship Road motel after advertising sex for $200 on Craigslist. Other cases have followed.

The prostitution cases in Hall have not involved underage girls. While the age of consent in Georgia is 16, prostitutes are considered underaged at 17 or younger. Runaways make up the majority of underage prostitutes, McCullough said.

McCullough said because Craigslist deals in legal trades, it “normalizes and legitimizes” ads for prostitution.

“It makes someone looking for sex not feel quite so badly about what they’re doing, and it makes it easier for them to keep doing it,” she said.

The website has faced mounting pressure to eliminate its adult services ads, with a lawsuit filed by the sheriff of Cook County, Ill., threats of criminal prosecution from South Carolina’s attorney general and criticism from former Atlanta mayor Shirley Franklin.

But while Craigslist groups its adult services ads geographically by major metropolitan areas like Atlanta, it’s not just an Atlanta problem, McCullough said. She said about 42 percent of the calls in the recent study come from north of the perimeter. Many prostitutes will agree to meet a john in a motel of his choosing, she said.

“Although it’s considered to be an inner city problem, the demand is being fueled from outside the inner city,” she said.