Robert Stevenson, 65, from Portsoy, is believed to have last been seen at about 16:00 on Thursday, driving south on the A947 between Banff and Macduff south of the Deveron Bridge.
His blue Dacia Duster's registration is R10AAT and has AA Taxis signage.
Mr Stevenson is described as white, 5ft 4in tall, of slim build, with short grey hair and a moustache.
He is believed to be wearing a white, pink and blue checked shirt.
Insp Megan Heathershaw said: "We would appeal to anyone who has seen the vehicle described to get in touch with police as soon as possible.
"It is out of character for Robert to go missing and as time goes by we are increasingly concerned for him and want to trace him to ensure he is safe and well.
"I would urge anyone who is out in the area, whether that is hiking or dog walking, to please be vigilant to the appeal to trace Robert and if they see him or his vehicle contact police on 101."
Police trying to trace a missing Aberdeenshire taxi driver have released an image of his car.