A masked man carrying a kitchen knife entered a Tesco Express in Northampton before making off empty handed.
The incident happened in Bordeaux Close, Duston, at about 2pm on Friday, August 18, Northamptonshire Police today revealed.
A spokesperson for the force said: "The offender was black, aged 20 to 30, of medium build and between 5ft 9in to 6ft.
"He wore a black balaclava, green or black hooded jacket and was carrying a green kitchen knife."
Witnesses or anyone with information about this incident is asked to contact police on 101 or Crimestoppers anonymously on 0800 555 111.