The suspect is described as a white man with pale skin, a scruffy black beard and a local accent. He is around 5ft 9in tall and was wearing a black puffer jacket with the hood up, grey jogging bottoms and white socks, but no shoes.
Officers are also trying to trace four people who were inside the store at the time of the robbery.
They are described as a white man with short brown hair wearing a red and blue sports jacket, a woman believed to be in her 50s who was around 6ft tall and wearing a grey sweater, and two younger girls who checked on the victim after the incident.
A spokesperson for Thames Valley Police said: “If you think that these people could be you or if you were in the area at this time and remember seeing a man walking with white socks and no shoes, please get in contact.”
