Police believe the trio approached a 20-year-old man in parklands off Governor Road in Braeside at about 11pm on March 31 during a privately organised music event.
The trio assaulted the victim before stealing a satchel containing a phone, cash and identity documents.
The trio fled the scene after the assault, according to police.
The 20-year-old victim was taken to hospital after suffering lacerations to his head and torso.
Police have released CCTV and images of three men they believe may be able to assist with their investigation.
