The suspect was playing a games machine in the bookies on Friday at around 7.20pm before approaching and threatening a female member of staff with the weapon and demanding cash.
He then made off with a three-figure sum of cash and a Scottish Poppy Appeal tin.
The member of staff and a customer were unharmed as a result of the incident but police say the employee was left “badly upset”.
Officers are now desperate to trace the man responsible as soon as possible.
The suspect is described as a white man in his late twenties to early thirties. He is around 5ft 10” to 6ft in height with a slim build. He has blue/green eyes that appeared bloodshot and brown greasy hair that was short at the sides and longer on top.
He was wearing a grey wind breaker style jacket, a black scarf, black jogging bottoms and black trainers with white soles. The suspect was noted to be smelling of cannabis.
Detective Inspector Paul Batten of Livingston CID said: “This was a frightening attack which has left a female member of staff badly upset.
“We are eager to trace the man responsible as soon as possible.
“I would ask anyone who was in the Hopetoun Street area on the evening on Friday 2nd November and saw anything suspicious, to get in touch with us immediately.”
Those with information are asked to contact officers at Livingston CID on 101, quoting incident number 3785 of November 2, or alternatively through Crimestoppers on 0800 555 111.
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