Illinois dad Brad Frakes says his daughter was using the app Musical.ly on his phone to create silly, mini music videos with her cousins.
That's when someone allegedly posing as a child began contacting her through the messaging function, asking the little girl to send secret photos without a t-shirt on.
After sharing his story on his Facebook page, thousands have come forward who have had the very same, horrifying experience.
"She had come to us and let us know that there was someone asking her to remove clothing for pictures and it wasn't right," said Frakes. "My message to parents would be to pay attention. Glad it didn't go further, we would be having a different conversation right now."
Frakes and his wife contacted police, who have been busy tracking down the IP address of the predator.
No matter the app, experts warn parents to always check the settings and make sure they are on "private."
Frakes said his next move is to create a place parents can go and share their experience and their warnings.