NEW YORK (CBSNewYork) — Officials in New Jersey on Thursday warned parents of a disturbing social media challenge that’s encouraging children to commit dangerous and sometimes violent acts.

The “Momo Challenge” encourages children to contact “Momo,” an anonymous cyberbully who uses a disturbingly ghoulish avatar, through Facebook or WhatsApp.

Momo asks children to play game, then encourages them to post pictures or videos of them committing violent acts.

If they refuse, Momo resorts to blackmail and threats.

The Monmouth County Prosecutor’s Office is warning parents to monitor their children’s online activity.