Police are appealing for witnesses following a robbery at NISA store in Chalcombe Avenue, Kingsthorpe, Northampton, which happened on Monday, 22 June.
Officers have released a CCTV image of a man seen loitering in front of the store who they would like to speak to in connection with the incident.
An offender went into the shop at about 9pm and threatened the staff with a knife, demanding cash. He fled empty-handed into Chalcombe Avenue.
He is described as a white man of about 5ft 7in with a medium build, in his late teens to early twenties with short dark hair and dark clothing.
Officers are keen to speak to a group of teenage girls who were seen talking to a man outside the shop at around the same time and urge them to get in touch.
Witnesses, or anyone who knows anything about this incident, can call Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111 or use the anonymous online form at www.crimestoppers-uk.org