The victim was walking along Sompting Road, near to Lancing railway station when he was approached by four men.
It happened at around 11pm on Thursday 15 April.
The men demanded the victim hand over any money, and one of the suspects produced a knife.
The victim’s wallet was taken, and he suffered a small wound to his hand during the incident.
The four suspects were travelling in a silver car, of similar shape to an old style Ford Fiesta, and left the scene in the vehicle in the direction of The Railway pub.
The men are described as white, aged in their 20s or 30s. One was wearing a black North Face jacket with the hood up and a blue surgical face mask. Another was wearing a purple jumper and grey bottoms, and a blue surgical face mask.
Anyone who witnessed the robbery or saw four men travelling in a similar vehicle in the area around that time is asked to get in touch.
Anyone with information is asked to contact police online or by calling 101 quoting serial 1063 of 16/04. Alternatively, information can be passed to police anonymously via the independent charity Crimestoppers online or by calling 0800 555 111.
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