Updated

Three Washington state teenagers who say they were sold online for sex have sued the website Backpage.com, accusing the website's owners of enabling their exploitation.

Two 13-year-old girls from Pierce County and one 15-year-old from King County, which encompasses Seattle, filed the lawsuit Friday in Pierce County Superior Court, The News Tribune of Tacoma reported Sunday.

Seattle attorney Liz McDougall, who represents Backpage's corporate owners, said the lawsuit will not pass legal muster and is barred by federal law. The site is owned by Village Voice Media in New York.

Backpage is a popular online destination for escort services. The company has been under heavy pressure to change the way it operates.

In May, the mayors of nearly 50 cities across the U.S. -- including New York, Los Angeles, Phoenix and Philadelphia -- signed a letter urging Village Voice Media to require identification for people posting escort ads on Backpage.com.

"Is it proper for some outfit, for some entity, to make millions of dollars not only in trafficking women, but even more importantly trafficking children?" asked Seattle attorney Mike Pfau, who with Erik Bauer represents the teens. "No. It is absolutely unacceptable."

The lawsuit alleges that photos of the underage girls in skimpy garb appeared in numerous ads on the site, paid for by their pimps. It accuses the owners of doing nothing to prevent it. The actions described in the complaint date to 2010.

The website requires ad buyers to click an on-screen button to verify that the users are 18 or older, but the lawsuit alleges it's not much of a deterrent, the News Tribune reported.

"Other than requiring the poster of the ad to agree to this term by 'clicking' on the posting rules page, Backpage.com does nothing to verify the age of the escorts who appear in its prostitution ads, even though it knows that pimps are usually the ones who create the ads, or force their minor sex slaves to do so," the complaint said.

McDougall, the company's attorney, offered sympathy for the young women.

"The stories of the girls identified in the complaint are tragedies. However, the commercial sex exploitation of children is an extremely complex problem on the streets and online, and it must be fought intelligently," McDougall wrote in an email to the newspaper.

"Backpage.com is at the forefront of fighting it intelligently online with a triple-tier prevention system and an unparalleled law enforcement support system."

Also on Friday, Backpage attorneys won a procedural victory in federal court. U.S. District Court Judge Ricardo Martinez granted an injunction that halts a new state law that would require classified advertising companies to verify the ages of people in sex-related advertisements.

Washington state Gov. Chris Gregoire signed the law this year to cut down on child sex trafficking. It had been scheduled to take effect in June.

The decision issued by U.S. District Court Judge Ricardo S. Martinez on Friday is temporary, until the full case can be heard in court.