According to Sussex Police, Robert Madejski, 30, has absconded from Ford Open Prison.
Madejski was last seen in the area near Worthing Library around 8am on Wednesday (May 11), police said.
Police revealed that he is part-way through a five-year sentence for fraud offences.
A spokesperson added: "He is described as white, 6ft 3in and of heavy build. He has brown eyes, a full beard and brown hair.
"Madejski is believed to have links to Kent as well as East Sussex, Essex, Lincolnshire and London."
Anyone who sees him is urged to dial 999.
Any other information on his whereabouts can be reported to police online or via dialling 101 and quoting serial 1378 of 11/05.