Police are continuing their enquiries to trace Nicholas Harper in the Helmsley area of North Yorkshire.
Mr Harper, 50, from Pickering, was last seen when he left for his work placement on the morning of Thursday February 7, but he did not arrive.
His vehicle was later found at Cowhouse Wood, north of Helmsley, where police searches are continuing today.
Inspector Dan Spence of North Yorkshire Police, said: “We remain very concerned for Nicholas’ safety and are continuing our searches of the area north of Helmsley today.
“Officers and volunteer search and rescue teams have been searching the area over the weekend with the help of police search dogs, drone cameras and the National Police Air Service helicopter. Specialist police search teams remain in the area today.
“Nicholas is an “ultra” runner and can run long distances, we are therefore appealing to outdoor enthusiasts who believe they may have seen Nicholas over the weekend, to please contact us along with anyone who is out and about in the area today.
“I would also like to appeal directly to Nicholas, your family, friends and colleagues are beside themselves with worry, if you see or hear this appeal, please contact us, you family or friends and let us know that you are safe.”
He is described as white, 5ft 5ins tall and of stocky build with dark brown short hair and a full beard. He was last seen wearing a three piece suit and shirt.
If anyone believes they have seen Mr Harper or has any information that could help the search, please call North Yorkshire Police on 101.
The incident number is 12190023491.