A man was held at knifepoint in a Northampton car park after his attacker approached him and asked for a lift.
The robbery happened in the Mayorhold Car Park, Lady's Lane, on May 11 at about 11.30pm.
A man was approached by another man and asked for a lift to Corby.
But he then demanded money from the victim and threatened him with a knife.
The suspect is described as a white man, aged 35-40, about 5ft 9in and of slim build. He had short, scruffy, black, untidy hair which was shorter at the back and sides. He had black stubble, a tanned complexion and a local accent. He was wearing dirty black jeans, a black hoodie with the hood up and a dark coloured body warmer.
Anyone who saw the incident or has information about what happened is asked to contact Northamptonshire Police on 101. Information can also be shared anonymously via Crimestoppers on 0800 555111.