Several big-name musicians have joined the fight to shut down the adult section on Backpage.com, a website featuring classified ads and owned by Village Voice Media.

The site has come under fire by a wide range of critics, including 48 attorneys general, who say Backpage is not doing enough to keep underage girls out of the sex ads.  Artists including former R.E.M. band mates, Pearl Jam and Alicia Keys have added their names to a petition on Change.org asking the website to stop running the ads.

In a statement, Mike Mills, formerly of R.E.M., said, "Village Voice Media has a history of being a strong advocate for the arts, reporting extensively on musicians and their work in its 13 weeklies across the country. That musicians are now speaking out … should send a clear message to the company that it needs to take action to ensure no child is sexually exploited through use of its site."

The Roots, Drive-By-Truckers and The Civil Wars have also added their names to the petition.

One industry analysis firm estimated that Backpage.com makes $22 million a year from the sale of ads in the adult category - and although the company disputed that number, they refused to give ABC News another figure.

Backpage.com did take "Nightline" into a screening room at Backpage, where employees look at every adult ad to try and identify underage girls. Backpage said they flag 400 suspicious ads a month and send them to the National Center for Missing and Exploited Children.

"It would be the wrong thing for Backpage to take down its adult category," said Liz McDougall, the attorney for Backpage.com told "Nightline." "Because you are losing a key tool for law enforcement to get insights into this illicit activity, to get greater data than has ever existed before, to locate, to identify the perpetrators and to rescue victims."

A bi-partisan group of U.S. senators also introduced a resolution this week asking Backpage to take down the ads.

Watch our original "Nightline" report: