Police say shortly before 9 p.m. Friday, a man with a handgun went inside Fenlon’s Family Market located at 114 Confederation Dr.
According to officials, the man fled on foot after the robbery and was last seen going northbound on Confederation Drive.
Police searched the area but couldn’t find him.
The suspect is described as a man between six-feet and six-feet-three-inches tall with a slim build.
He was wearing a dark blue hoodie, dark pants, tan-coloured gloves and black shoes with white trim.
Police say the store employee was not injured.
Anyone with further information is asked to contact St. Thomas police at 519-631-1224 or Crime Stoppers at 1-800-222-TIPS (8477).