The man, armed with a weapon, went into the Family Shopper store in Causeyside Street, Paisley, at about 8.10pm on Sunday and threatened staff before making off with money.
He was with another man who held the shop door open for him.
Both men ran off towards the Gordon Street area of the Renfrewshire town.
Police are appealing for information about the incident.
The first man is described as in his early 20s, about 5ft 8ins and with dark brown hair.
He was wearing a black body warmer with a grey hood over a green pilot-style jacket and dark grey jogging bottoms.
The man who held the door open was about 6ft and wore dark clothing with the hood up.
Detective Constable Raymond Brownlow said: “Thankfully nobody was injured during this incident but it was still very frightening for those in the store at the time.
“I would like to speak to anyone who may have seen two men matching these descriptions in the surrounding area last night.”