Police have been told a social media post is what prompted three teenage girls to attack a fourth in Blue Haven last night.
Offices are investigating reports the trio aged between 13 and 15 confronted the 15-year-old victim at a skate park on Colorado Drive around 5pm, threatening her with a knife.
They say the girl was then punched and had her head pushed to the concrete before the offenders left the scene.
The 15-year-old was taken to Wyong Hospital with minor injuries, and has reportedly identified the others involved.
Police now want any witnesses to come forward - call CrimeStoppers if you can help out.