Police in Iowa warned parents this week of a scam that involves strangers soliciting nude photos from teenage girls on Facebook. Officials say they are investigating five cases in Johnston, Iowa, Ankeny, and several other communities.

Officials say the victims in each instance accept a Facebook friend request from a stranger claiming to be a photographer or a representative from a modeling agency. The perpetrator’s profile also shows that they have mutual friends. Once the crook receives nude photos, he or she threatens to spam the victim’s friends and family with the picture unless the victim sends more. A 14-year-old girl has even fallen prey to this sickening scam.

“It is shocking for parents. No one wants to hear about kids sending compromising photos to a stranger,” Sgt. Lynn Aswegan of the Johnston Police Department said. “They’re using photos as ransom using them to extort additional photos from them… Most girls have gotten scared, embarrassed, sent more photos hoping to take care of the problem.”

While there’s no method in place on the site for preventing underage users from acting independently, police say that parents should talk to their children about online behavior and even monitor their activity if necessary.