Sussex Police is concerned for a missing Chichester man, who could be travelling on trains.
Police said Richard Alexander, 30, was last seen on Monday afternoon (January 14).
A spokesman added: "He is dependent on medication and he is not believed to have taken any with him.
"Richard is white, 6' 1", of slim build and with short brown hair. He was last seen wearing black tracksuit bottoms, a white t-shirt, grey coat, black shoes and carrying a bag.
"He will often travel on public transport, in particular the train."
Anyone who has seen Richard or who knows of his whereabouts, is asked to contact police online or ring 101 quoting serial 1153 of 14/01.