A hitch-hiker put a knife to a driver's throat and stole £50.
He was picked up in Lansdowne Place, Hove, and driven to Edward Street, Brighton, where the offence took place.
The robber made the victim drive to the seafront, near East Street, Brighton, where he got out and fled.
He was about 26, 5ft 11in tall with brown-ginger hair and a spotty face.
He wore a dark blue hat, blue jacket, blue trousers and white trainers.
Witnesses or anyone with information about the robbery on February 4 should contact Detective Constable Ian Still on 0845 6070999.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article