The 74-year-old retired accountant and businessman has not been seen since he left his home in Cross Hills on Monday, saying he was going for a walk in the Skipton area.
The search area is now Great Whernside and Kettlewell in the Yorkshire Dales.
David speaks with a stutter and is wearing the same blue waterproof jacket as in the photograph.
He told his family he would only be away for up to five hours, and drove into Craven in a black Volvo V60.
North Yorkshire Police said: “We are currently carrying out enquiries to locate him but are growing increasingly concerned for his welfare.
“To assist with the search, we have called in the Upper Wharfdale Fell Rescue association and the RAF who are assisting with a helicopter.
“David is described as wearing a blue jacket, red trousers, a orange and brown striped scarf and he was carrying a red and black rucksack.
“Anyone who has seen David, or his vehicle, or has information that could assist us, is asked to call 101. If you have an immediate sighting please dial 999”