Last Wednesday night a man in a hoodie robbed Thirsty Liquor on Glenfield on the corner of Chivalry Rd and Diana Dr.
Police have released CCTV footage of the incident robberies, which they described as "frightening".
"It's the second time in a week that an offender fitting the description has robbed a liquor store in the area and police want to identify and apprehend him as soon as possible," a police spokesperson said.
"The owner was sitting behind the counter when the man, armed with a long knife, entered the store, threatened her with the knife and demanded money. As the footage shows, she complied fully and he fled."
Police and dogs converged on the area but the robber could not be found.
A similar incident occurred on Sunday 26 July at the Harbour City Liquor Store on View Road in Glenfield.
At 3.45pm a man fitting the same description as the earlier robbery entered the shop and threatened the employee with a knife, he demanded money.
The employee handed over the money and he fled. No CCTV footage is available of this incident.
"This is obviously worrying. The footage speaks for itself and the victim has done very well to stay calm and hand over the money," said Detective Kelly Farrant.
"We're very keen to prevent any further offending and if anyone knows who this is, please get in touch with us."
Anybody with information regarding the whereabouts of David Cerven is asked to contact the North Shore CIB on 09 477 5261 or to pass on information anonymously, contact Crimestoppers on 0800 555 111.