Despite extensive searches Gary Davison (inset) has not been found

Hundreds of rescuers spent days looking without success for Gary Davison, 44, from Slough, Berkshire.

Sam Roberts, a Snowdonia National Park warden with 33 years' experience, said a failed search was unusual.

"There are holes and cracks someone could fall in and not be seen as close as 50 yards from the path," he said.

Mr Davison, a draughtsman, was last seen on 2 January after his car was found parked nearby.

We're always getting calls from people saying 'little Johnny is lost,' and when we ask where they were walking they say, 'in Snowdonia' - and Snowdonia is a very big place Sam Roberts, warden

"People get lost all the time, but they usually turn up, a case like this is unusual," said Mr Roberts.

"All we know for certain is that this man parked his car at Pen y Pass and was seen starting off up Snowdon," said Mr Roberts, a senior warden in the park's northern area.

"It is unusual for people to disappear, they usually turn up somewhere," he added.

As always, said Mr Roberts, the advice to walkers was to leave details of their intended route.

There are two to three paths walkers usually follow from Pen y Pass to the summit, but some routes are more challenging than others. Off the paths the landscape can be "desolate."

Walkers on the path from Pen Y Pass to the summit

"It is also a vast and difficult area to search," he added.

In fine weather, and even in the middle of winter, there can be 1,000 people starting from the Pen y Pass car park - where the missing walker's car was found.

"People check the weather report early then travel from Liverpool, Manchester and even Birmingham in a couple of hours," said Mr Roberts.

Deep crevice

"Pen y Pass car park which holds between 60 - 80 cars can be full by nine (in the morning)."

He recalled two other cases where people were not been found for quite a long time on the mountain.

One was at the beginning of his career in the park when a walker disappeared in the Ogwen area.

The body was found, by complete chance, by a walker who happened to look into a deep crevice three months later.

On another occasion walkers came across a body of a person who had not been reported missing.

The guess was that it had lain on the mountain for about six months before being discovered.

"We're always getting calls from people saying 'little Johnny' is lost, and when we ask where they were walking they say, 'in Snowdonia' - and Snowdonia is a very big place."