A 44-year-old man was threatened and robbed of his wallet and mobile phone in Hove.
The robber threatened to stab the victim in the Palmeira Square area between 3.30am and 4am on Tuesday 7 September.
Sussex Police said that the offender was described as a black male, 25 to 30 years of age, 5ft 8in to 6 ft tall and dressed all in black.
No weapon was seen and the victim was uninjured.
Any witnesses to this incident, which may have taken place in a bus shelter, are asked to contact Detective Constable Leon Ryan from Brighton CID on 0845 6070999.