Kirklees District CID would like to speak to anyone who has information about the incident which took place between 7.40pm and 7.44pm at the Co-op on Nab Lane on Sunday November 18.
The suspect entered the store and approached one of the workers – a woman in her 20s - behind the counter, before producing a knife and demanding she opened the till.
The suspect then made off from the shop in the direction of The Knowl with a quantity of cash.
Enquiries remain ongoing by detectives in Kirklees CID.
A Spokesperson for the Co-op, confirmed: “There was an incident at our Nab Lane, Mirfield store at 8pm on Sunday when intruders entered the store.
"We appeal for anyone with information to come forward to the Police, who are investigating. The store re-opened as normal yesterday morning to serve the community.”
Anyone with information or anyone who witnessed anyone acting suspiciously in the area at the time of the incident is asked to contact police on 101, quoting crime reference 13180579601.
Information can also be passed anonymously to independent charity Crimestoppers on 0800 555 111.