Documentarian Mary Mazzio talks to PEOPLE about her new documentary, I am Jane Doe, on the sex trafficking industry

Documentarian Mary Mazzio has met several women and girls who survived the sex trafficking industry — and one thing that surprised her was how many of them were willing to go on camera to share their stories.

“Every one of them looked at me and said, ‘So it won’t happen to my little sister or my friend,’ ” Mazzio recalls.

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Another girl looked her in the eye and said, “‘I’m doing this so it doesn’t happen to your daughter.’ ”

Their collected accounts are the focus of Mazzio’s documentary I Am Jane Doe, which opens Friday. The title is a reference to the name adopted by an anonymous party in a lawsuit or crime — which is fitting, as multiple survivors are suing Backpage.com. They argue that the company’s CEO and former owners knowingly permitted the sale of underage girls for sex.

Representatives for Backpage.com and its executives have said a federal law protects them from third-party posters to the site. An attorney for the site claims the now-suspended “adult section” was actually an aid to police.

One of the women featured in Jane Doe and who is suing Backpage.com is J.S., who agreed to share her story in this week’s issue of PEOPLE. She and her family filed a lawsuit in the state of Washington in 2010 after J.S. was seduced as a teenager by a man twice her age, sold for sex and eventually rescued in a police sting operation.

It has been seven years, and her case is headed for trial in the spring.

• For more on J.S. and her fight against sex trafficking, subscribe now to PEOPLE or pick up this week’s issue, on newsstands Friday.

“As a family, you really feel the personal toll that it takes,” J.S.’ father, Tom, tells PEOPLE. “We’ve had a lot of support. It’s the kids and girls out there that don’t have a voice that we’re trying to represent.”

Mazzio says her film is built on their courage and the courage of the other women.