Police are searching for a 38-year-old Portuguese man believed to suffer from autism.
A spokesman for Sussex Police said Roberto Correia went missing after he left his family home in Weald Drive, Furnace Green, on a bicycle at around 9.30am on May 22.
PC Matt Gowin said: “Along with his family and friends, we are growing increasingly worried about his whereabouts and his health.
“He is not believed to have had much money and does not have credit or debit cards, so there is a fear that he is probably sleeping rough.
“Lately, he has become very interested in cruise ships and we would especially ask anyone living along the coast and near to ports to be looking out for him.”
Roberto was described as white with a tanned complexion, 6’ 2”, of medium build with short shaven black hair.
The spokesman said he may be wearing blue jeans or grey jogging bottoms, a grey Adidas hooded top with red stripes on the sleeves and white Adidas trainers with green detail.
His bicycle was a distinctive black and bright orange Carrera mountain bike.
The spokesman added: “He does not leave home very often on his own, but is very enthusiastic about visiting museums, especially in London and was found in Liverpool when he went missing once before.”
Anyone with information was asked to call Sussex Police on 101 quoting serial 766 of 22/05.