Cardinia Crime Investigation Unit detectives are appealing for public assistance to help identify two males following an attempted armed robbery on 5 August, Victoria Police say.
Police have been told a 17-year-old boy and his friend were approached by two males, believed to be aged in their late teens, while at a post office in Pakenham.
The pair accompanied the teens as they walked along the Pakenham Creek Reserve Trail about 10.30pm.
One of the males then produced a knife and demanded money from the victim, who ran from the scene and was chased a short distance.
The offenders then fled empty-handed.
The victim and his friend were not injured.
Police have released an image of two males who they believe can assist with their enquiries.
Both have been perceived as Caucasian in appearance and about 178cm tall.
One had long black hair and was wearing grey tracksuit pants, a black top and light-coloured cap.
The other had light brown hair and was wearing blue jeans, brown boots and a cap.
Anyone with information or who recognises the pair is urged to contact Crime Stoppers.