The man entered the shop on North Rd at Invercargill about 3am on Saturday, November 9.
He threatened two staff members with a knife before leaving with cash and pouches of tobacco.
The alleged offender was described as a Pakeha man in his late teens or early 20s, about 182cm tall and of a thin build.
He was wearing a white hoodie, light blue or grey jeans or chinos, black gloves, a black balaclava or stocking, black sunglasses, and black shoes with no brand markings.
He was wielding a long, orange-handled knife.
Following the robbery he was seen heading north on North Rd.
-Police - 105;
-Crimestoppers - 0800 555 111.