Harrison Fast was part of a group of six who were speedflying – a form of paragliding, sometimes with skis – in the Jungfrau region, in the Bernese Oberland, on Saturday.

After a surprise storm hit the group they became separated. Some of the group were rescued by a helicopter and others were able to get to safety themselves, but Fast never reached the planned meeting point.

Speaking to news agency ATS on Tuesday, Christoph Gnägi, spokesman for Bern cantonal police, said that Swiss rescue services launched a search operation but it had to be abandoned due to bad weather and high winds on Sunday and Monday.

“We did everything that was humanly possible,” said Gnägi.

The search zone is very steep and full of deep crevasses, he added.

The family of the missing man, based in Colorado, US, have set up a fundraising page to raise money to conduct a private search of the area.

On Wednesday morning the youcaring.com page had more than $48,000 pledged to help the family fund a search using drones, helicopters and other technology.

But it hasn’t been easy. Speaking to The Local, Harrison Fast’s sister Suzanne Fast said search and rescue workers will not continue to search without official permission from local authorities.

“Private search is difficult because we can pay a helicopter pilot to go up, but we cannot pay for search and rescue people to go up. A pilot on his own isn't much help,” she said.

“I know the [Swiss mountain rescue service] Rega and local authorities tried very hard for us the first few days but since will not do anything. They don't understand we want to bring him home no matter what.”

“Although we understand that the local authorities think it's useless, a waste of our time and money to continue to look, we need to bring Harrison back.”

The family is now paying for drones to search the area instead.

“But that has its own difficulty with battery life and from my understanding you still have to control them from an area that you can see them.

“As of right now we don't want to risk anyone trying to go in by foot because of the dangers.”