Police have released an image of a man who exposed himself to a teenage boy in Altona on October 11.

Altona North detectives say a 15-year-old boy was walking through a park near Harrington Square shopping centre about 9.20am.

He saw a man standing near a residential fence who was holding a phone in front of him with one hand while masturbating.

Investigators have released a computer-generated image of a man who may be able to assist with their enquiries.

The man is described as Caucasian, about 170 centimetres tall, aged in his 30s, with a medium build and short hair.

He was wearing a black hooded jumper with a white motif on the back, brown shorts and work boots.

Anyone with information or who witnessed the wilful and obscene exposure should contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au