A missing 76-year-old man may have walked from Thame 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, who is 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.
“I would also like to appeal directly to Alan to say that his family and friends are very worried about him and I would ask him to get in touch with his family or the police as soon as possible.”
Call police on 101 with information.