Investigators have been told the victim, a then 18-year-old woman, was in attendance at a music festival on 29 December.
The woman was searching the grounds for her friends about 9pm, when a male unknown to her offered assistance.
They walked around the festival grounds but were unable to find her friends.
The unknown man then pushed her into a tent and sexually assaulted her.
Detectives have released a digital face image of a man they believe may be able to assist with their enquiries.
He is perceived to be Caucasian in appearance, was aged in his early 20s, had a lean muscular build, a very pale complexion, and short wavy dark brown hair.
The man was wearing mid-thigh length denim shorts, a button-down top with a pattern and had black Ray Ban Wayfarer sunglasses on his head.
Anyone who recognises the man or with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au