Melbourne Embona Taskforce detectives are investigating a robbery and assault on the grounds of an educational facility on La Trobe Street Melbourne on 1 November.
Investigators have been told three friends were playing on a basketball court about 8.30pm when they noticed a group of people going through their bags.
The victims confronted the males who then punched and kicked the victims.
A male unknown to the victims tried to intervene and was also assaulted.
This man left the scene and his details are unknown at this stage.
Police have released an image of a man they believe can assist them with their enquiries.
Police would also like to speak to the unknown man who tried to help and was assaulted.
Investigators are urging anyone with information or who witnessed the incident to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au