The 49-year-old was reported missing from Duncairn Gardens in the north Belfast around 11.30 pm on Monday night.
A PSNI spokesperson said: “John “Jackie” McWilliams has been reported missing from Duncairn Gdns, Belfast.
“He is described as 5′ 10” tall and of medium build.
“He was last seen at 11.30 pm on Monday night and his family are very worried.
“Jackie’s health isn’t good and he suffers from confusion.
“Anyone with information about his whereabouts is asked to ring 101 quoting ref 223-18/9/18.”