Knox police are investigating an attempted armed robbery at a Wantirna milk bar on 27 June.
Detectives believe a man entered the Crestdale Road milk bar at 7.30 pm armed with an imitation firearm.
He made a demand for cash before being chased from the store by the attendant.
The offender is described as Caucasian, between 15 and 18-years-old, approximately 170 centimetres tall, with a slim build.
He was wearing a distinctive patterned top, tracksuit pants, and dark shoes.
Police have released three images of a man they believe can assist with their enquiries.