The incident happened at around 9.55pm on Saturday July 30 in Ayrshire.
A 55-year-old man was walking on Afton Street in Stevenston when he was approached by another man.
He was then threatened by the individual, who stole a sum of money from him.
The suspect is described as being about 6ft tall and wearing dark clothing and a balaclava.
Detective Sergeant Andrew Dunlop, of North Ayrshire CID, said: “The victim was not injured but has been left shaken by this incident.
“Extensive investigations are being carried out to identify the person responsible.
“We are keen to speak to anyone who was in the area at the time or saw someone matching the description of the suspect either before or after the incident.
“I would ask anyone with a dash cam or doorbell to check their footage as it could prove important in our investigations.
“Anyone with information can call 101 quoting reference 3920 of Saturday 30 July 2022 or call Crimestoppers anonymously on 0800 555 111.”