Michael Rosse was at his home in Worthing at around 10.30am on Tuesday (31 July), police said.
He was seen at 7pm at Larkfield Priory Hotel in Maidstone in Kent the next day (Wednesday, August 1).
However officers believe he could be using a variety of other names including Alan Fraser, Mr Hardy, Michael Heenes, Ross Fraser, police said.
Police said: “Michael takes regular medication and it is not believed he has taken any with him.
“He is white, 5ft 8ins, with short dark but greying hair and blue eyes.
“Michael was last seen wearing a long-sleeved dark blue shirt, blue jeans and brown shoes.”
Anyone who sees Michael should call 999 immediately.
Anyone with information on where he could be or any previous sightings, report online or call 101 quoting reference 648 of 31/07.