BOSTON — Attorney General Maura Healey threw her support behind a civil lawsuit aimed at a website that carries personal ads for people looking for sex, alleging the company assists in human trafficking.

Healey filed a brief Friday in U.S. District Court urging the court not to dismiss the lawsuit against Backpage.com, filed by three women who say they were sold for sex on the website when they were as young as 15.

Healey argues that websites that knowingly support human trafficking should not be immune from liability.

Backpage.com has asked the court to dismiss the case. Lawyers for the website have said that the company disputes the allegations and does more than any other online classified site to prevent the trafficking of minors.

Healey said she felt it was important for her office and the state to weigh in on the lawsuit, given what she said is the serious problem of human trafficking and sexual exploitation in Massachusetts.

Lawyers for the website in a similar lawsuit in Seattle have argued the suit should be thrown out because the website didn’t write the ads, so it’s not liable, pointing to the federal Communications Decency Act. They argued Congress wrote the act to preserve free speech on the Internet by giving immunity to websites for items posted by users or members of sites.