Three state attorneys general and representatives from six other states on Tuesday pressed lawyers from Craigslist to permanently remove the site's erotic services section.
Leading the charge at the closed meeting in Manhattan was Connecticut's top prosecutor, Richard Blumenthal, reports CBS News correspondent Kelly Wallace.
"No question, absolutely none, that Craigslist is operating an online brothel here," Blumenthal said. "We're going after them to persuade them they ought to do the right thing, cooperate, and eliminate the ads."
South Carolina Attorney General Henry McMaster went further: Craigslist must remove all prostitution ads and pornography or Craigslist executives themselves will be prosecuted.
"It is nothing but filth," McMaster said. "It is advertisement for prostitution. It is ugly. It is harmful."
Can Craigslist be held criminally liable or sued for having illegal ads on its site? Not under current federal law, which grants immunity to sites like Craigslist for posting content it didn't create.
"Congress' rationale, which I think was a good one, that we want to not make illegal content legal or somehow inexcusable but place the onus on the people who are behaving badly in the first place," said Matt Zimmerman, a senior staff attorney with the Electronic Frontier Foundation.
The pressure on the classified online ad site, which gets 30 million postings a month, has grown in recent weeks after medical student Philip Markoff was accused of robbing two women, and killing another, all of whom he met on Craigslist, and a New York radio reporter was killed by a teenager who allegedly responded to a Craigslist advertisement.
In a statement, Craigslist's CEO Jim Buckmaster said Tuesday's meeting was productive.
"We're optimistic that our shared concerns can be addressed...without compromising the quintessentially American values of free speech embodied in our constitution," Buckmaster said.
In November, Craigslist, at the urging of the states attorneys general, agreed to begin requiring a working phone number, a credit card, and a $5 fee for anyone using the erotic services section.
Blumenthal said that the action hasn't gone far enough and that if Craigslist doesn't respond positively in days, not months, the states' prosecutors will consider trying to change the law or finding another route to legal action against the site.