Police are now appealing to walkers and farmers to hunt for clothing, which they believe may have been discarded by the 26-year-old following his disappearance last month.

It is thought Mr Thomson, who takes medication for severe migraines after being left with brain injuries following a car crash in 2005, may have developed hypothermia, which can lead the person to feel hot and subsequently take their clothes off.

A dozen of his friends met in Scorton – where he was last seen on CCTV footage – on Sunday to search fields.

Chris Walker, 28, from Kirkham, said: "We searched the fields from 10am and didn't stop until 4.30pm. It's a big area that we can eliminate. But there was no sign of anything. Everyone was a bit upset that we couldn't find anything.

"I like to think he is somewhere. He's a good lad. We miss him."

Another friend drove Mr Thomson's mum, Maggie Hanson, around Preesall and Pilling to ask people if they had seen him.

And another, Angela McAinsh, 30, from Blackpool, said: "I've got posters that I carry around with me.

"We met a lot of people out there and they were lovely, as helpful as they could be. It's just not knowing. It's been two weeks so we can't give up."

Miss McAinsh now plans to email haulage companies with Mr Thomson's photo.

She added: "Maybe someone has picked him up but he's confused and doesn't know who he is. We are still clinging on to hope."

Mr Thomson left his home on Nightingale Drive in Poulton on Saturday January 16.

He was seen in Bispham and then abandoned his blue Vauxhall Astra van in Station Lane, Scorton, in the early hours of Sunday January 17.

He has not been seen since.

Police have been scouring nearby fields and an underwater search team has been working in the River Wyre.

Insp Dave Tuer, from Lancaster Police, said: "Our last sighting of David is at 6am on Sunday near to the Six Arches caravan park in Scorton, where we have him on CCTV. At this time he was cold and wet.

"He was obviously confused and may well have wondered off into the surrounding woods. It is quite possible that he would have been suffering from hypothermia."

Walkers and farmers are being asked to assist with the search.

Insp Tuer added: "We ask that farmers check their fields, woods and outbuildings for David's clothing and those out walking in the area surrounding Scorton, Ellel and Garstang also keep their eyes open. Sadly, if David has developed hypothermia then our hopes of finding him alive are fading fast."

Mr Thomson is 5ft 8in, white, with brown cropped hair. He was wearing a parka style hooded jacket and black Rockport boots when he disappeared.

Call police on (01524) 63333.