"Craigslist is responsible for the types of advertisements it allows, and it is imperative that Craigslist agree to tougher restrictions and to remove ads for illegal activities from its site," Koster said.
He said his office has been investigating the site and has found many instances where advertisements remain on the site even after being flagged as illegal.
"Our investigators found advertisements that clearly were offering sex-for-money or seeking a sex-for-money relationship on Craigslist's Kansas City, St. Louis, Columbia/Jefferson City and Springfield sites," Koster said."These arrangements advertised are not only illegal but dangerous, and we aim to stop this type of advertising in Missouri."
In an interview with ABC Nightline's Martin Bashir, Craigslist CEO Jim Buckmaster said the company is shocked and horrified whenever it hears of the site being used to facilitate crime.
Craig Newmark, Craiglist's founder, said that if a posting on the site is advertising an illegal activity, he wants help from the user community to remove it immediately, but he doesn't believe the site facilitates prostitution he told Bashir.
Newmark said the site would change its posting policies based on feedback from its user community -- feedback that Newmark noted changes over time. He noted that law enforcement officials are part of that community. Craigslist will hear from that part Tuesday.
Last November, the company reached a settlement with 43 attorneys general that required it to implement a variety of measures that would help identify providers of prostitution and related services. Among the measures to be implemented as part of the agreement are requiring a "small fee" charged to a credit card and a valid phone number be provided by advertisers of erotic services. In addition, the site supports industry standards for content flagging to prevent minors from accessing adult content on its site. In a post to the company's blog following the November settlement, Buckmaster expected requiring a credit card and charging the fee would result in few illicit ads remaining. "For those that do persist, telephone and credit card information will be available to law enforcement via subpoena," he said.
In a letter he sent Craigslist in April, Connecticut Attorney General Richard Blumenthal proposed the company begin implementing several measures immediately in order to combat the presence of pornography and prostitution on the site. Proposed measures include eliminating images in the "erotic services" section, hire staff to screen the site for ads that blatantly violate the site's terms of service, charge the credit cards of users who violate Craigslist's terms of service "a significant fee" and provide financial incentives for users to report advertisements that violate Craigslist's terms of service.