Robin Auld, aged 82, from Henley-on-Thames, was last seen at 3.30pm on Thursday (5/3) in Portland Road, in the Notting Hill area of London.
He had left London to travel towards Henley-on-Thames in a maroon coloured Volvo V50.
Robin is described as white, with grey hair, around 5ft 10ins tall, of a slim build, and occasionally wears glasses.
He was dressed in a tweed jacket and cap when he was last seen.
Investigating officer, Inspector Stephen Clewlow, of High Wycombe police station, said: “We believe that Robin was taking a route he regularly took between London and Henley-on-Thames. However he did not arrive in Henley-on-Thames.
“Robin would take this route on a regular basis and it is extremely out of character for him to have gone missing.
“If anyone thinks they have seen Robin, or believes that they may have information on his whereabouts, please contact Thames Valley Police on 101, quoting 43200076216.
“Alternatively, if Robin sees this message, please make contact with your family or the police, as we are concerned about you.”