A 15-year-old boy was left badly shaken up when the USave store he was working in was held up by an armed robber.
Another member of staff was also menaced with what appeared to be a gun in the incident in Belville Street, Greenock.
The brazen bandit struck in broad daylight at around 3.15pm on Saturday 10 August.
He is described as white, about 5ft 10in tall, aged in his late teens to early 20s, with a medium build.
The thug, who made off with a two-figure sum of money, was wearing a dark hooded top with the hood up, dark trousers and had a scarf over his face.
Police conducted door-to-door enquiries and are reviewing CCTV footage in the wake of the robbery.
Appealing for anyone who was in the area at the time of the incident to get in touch, Detective Sergeant Stuart Young asked: “Did you notice anyone hanging around outside the shop, did anything strike you as odd or suspicious? Please think back and consider if you saw anything which could help our investigation.”