A missing 76-year-old man may have walked to Bicester, police believe.
Alan Battista, has not been seen since he left his Thame home on Wednesday night wearing a navy blue anorak and trousers.
Insp Nick Deacon, of Thames Valley Police, leading the search, said: “We are becoming increasingly concerned for Mr Battista’s welfare.
“We believe he might have walked from Thame to Bicester and then got a bus to Milton Keynes.”
Anyone with information is asked to call police on 101 with information.