ROSEVILLE (CBS13) — A Roseville man is behind bars after Facebook contacted authorities about some illegal activity found on the social media site.

Roseville Police say they usually have to do most of the digging when it comes to crimes on social media.

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“It’s great to know they are monitoring their absolutely enormous site looking for this kind of thing and protecting kids,” police spokeswoman Dee Dee Gunther said.

Anthony Madderra, 21, was arrested thanks to a tip to from Facebook.

The site reportedly detected some illegal activity involving an adult male from Roseville and forwarded the findings to the National Center for Missing and Exploited Children, who then sent the information over to the Roseville Police Department.

It wasn’t until that tip that investigators started looking into the case and discovered Madderra would troll the popular social media site for underage girls and persuade them to take pornographic photos of themselves and send them to him.

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“We found out he had contacted two 15-year-old girls via Facebook,” she said.

Gunther says Madderra’s crime spanned several states. One alleged teenage victim was from Sacramento, the other from Oklahoma.

Gunther says it’s a good reminder to parents to be aware of their kids’ online activity.

“I watch the Facebook really closely about those things,” parent Vickie Duran said.

She says Facebook’s quick actions give her some peace of mind that someone else is also watching out for her kids on social media.

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Police are concerned there may be more victims.