Prosecutors from around the world say the fight against sex trafficking is moving online as traffickers use popular websites to advertise sexual services.

They talked Friday about how they can crack down on the problem at an international sex trafficking summit in Waikiki that drew prosecutors from Asia, the U.S. and Canada.

The challenges each nation faces are similar, and victims are often unwilling to cooperate with investigators because they’ve endured a history of abuse, said Jackie Lacey, Los Angeles County’s district attorney.

“Most of this is underground,” Lacey said. “It’s not like in the ’80s and ’90s where women were on the street. It’s all done by social media, cellphones, emails, text messages.”

Michael Ramos, president of the National District Attorneys Association, said he plans to push for legislation in the United States to make it illegal to use websites to solicit illegal sex and to hold internet companies accountable for sex trafficking that occurs on their platforms.

“There should be some place that says you need to do a better job with the content that’s on your promotional site,” Ramos said. “It’s just so easy right now … Instead of having prostitutes out on the corner like they used to in a red light district, now they just go online, they hit a button, and it’s like ordering a pizza.”

Other law enforcement officers, such as Honolulu Prosecutor Keith Kaneshiro, said websites that allow sex ads have helped officers catch traffickers by identifying locations where there’s a problem.

Sonia Paquet, a Canadian prosecutor, talked about how prostitution is illegal but there’s little enforcement. She said online reviews of establishments are out in the open, and she pulled up one on her phone.

“If we go on the internet site, we see the girls naked,” she said. “They are from everywhere around the world.”

Prosecutors from Canada, China, Japan, Palau, the Philippines, South Korea, Taiwan and Thailand attended the summit. American prosecutors attended from more than a dozen states including Arkansas, California, Hawaii, Illinois, Kansas, Louisiana, Massachusetts, Nebraska, New York, Nevada, Oregon, Virginia, Washington and Washington, D.C.