The 74-year-old retired accountant left his home in Cross Hills, Keighley, on Monday, telling his family he was going for a walk in the Skipton area and would be away for around five hours.
He did not return and a huge search involving the police, RAF and several mountain rescue teams is still ongoing.
Mr McCartney is described as speaking with a stammer and may appear confused to anyone who encounters him.
North Yorkshire Police confirmed on Friday that they have found his black Volvo parked in the Kettlewell area.
The experienced walker was supposed to be doing a 'recce' of an eight-mile route.
He left home wearing a blue waterproof jacket, red trousers and an orange and brown scarf. He was carrying a red and black rucksack.
Extensive resources have been allocated in the search to find him. Today, officers have concentrated on the Great Whernside area and have used two police drones to allow them to view aerial footage of vast open areas. Officers on the ground have been assisted by the National Police Air Service helicopter, search dogs, volunteer mountain rescue teams and the RAF.
Critical Incident Inspector Martin Smith from North Yorkshire Police said “We are extremely concerned for David’s welfare and significant multi-agency searches are planned for across the weekend. I urge anyone who is out walking in the Great Whernside, Kettlewell, Buckden, Grassington and Angram Reservoir areas this weekend to be vigilant and to report any immediate sightings of anyone matching David's description to 999.”