The incident happened at a store on Sewerby Road around 1.15pm on Monday November 25.
It was reported that he was holding what has been described as a blade while he demanded money from the till.
The man stole four bottles of whiskey before running out of the shop down an alleyway. No-one was hurt during the incident.
The man has been described as being in his mid to late 20s, around 6 feet tall and wearing all black clothing. He had a hood pulled tight over his face which was covered with a scarf.
Police have already got some information about who this suspect might be, but are appealing for any further information to help them catch him.
Anyone with information is asked to contact Humberside Police on 101 quoting crime reference 16/128838/19.