Keith Michael Jervis, 53, was last seen on February 16 at the caravan park, Corner Meadow, Farnborough Road, Mollington, near Banbury.
He may have been in the Milton Keynes and Newport Pagnell area and is known to have links to Pembroke Dock in South West Wales.
Keith is described as white, 5ft 6ins tall and medium build with dark brown curly hair.
Keith left the caravan park in a Silver Toyota Hilux index BJ65EFT. The car has now been located at a local retail park locked and secure. Both known mobile phones for him were within the vehicle.
It is believed Mr Jervis may have travelled to Harrow, London
Det Sgt Mark Personius leading the search said: “We are very concerned for Keith and urge anyone who knows where he might be to contact us as a matter of urgency.
“We believe he visited Newport Pagnell Services on Wednesday February 22 as money was withdrawn from his bank account but there has been no contact since.
“Having spoken to those who know him, no one is aware of any plans he made to leave the area.”
Anyone who has seen Keith or knows of his whereabouts is asked to call Thames Valley Police on 101 immediately.