Arguing that trafficking and child exploitation are rare on his site, Buckmaster said Craigslist already has a zero-tolerance policy for crime.

"We work tirelessly with law enforcement to ensure any such victim receives the assistance they deserve and anyone responsible is prosecuted," he wrote.

In her original letter to Craigslist, Speier said she was moved to write the company after seeing a newspaper ad by the The Rebecca Project, a group that advocates for policies to help vulnerable women and girls. The ad features letters from two women who say they were been forced into prostitution after meeting men over Craigslist. "Craig, shut down the adult services section," they write.

Craigslist’s adult services section was started last year to replace the “erotic services,” which underwent criticism for providing a go-to place for human trafficking. Adult services is a portal to  “massage” and “spa” ads that still, in many cases, thinly veil the pursued sale of sex.