The family of an American extreme sports enthusiast who went missing in the Swiss Alps over the weekend said Wednesday they're holding out hope that he's still alive.

Harrison Fast of Boulder, Colorado, was speed flying on the Jungfrau mountain in central Switzerland when the group he was with lost sight of him amid bad weather. Speed flyers run or ski down slopes and then use special parachutes designed to let them fly fast and close to the ground.

Cassie Carothers, a cousin, said she and Fast's mother traveled to Switzerland to organize a private search.

"We are holding out hope and wishing for a miracle that perhaps he made it down," she told The Associated Press in a telephone interview.

Swiss police said they called off their "active search" for Fast on Tuesday. The 28-year-old had recently arrived in the Bernese Alps, a popular place for thrill seekers because of its majestic mountains, beautiful panoramas and relatively lax laws on extreme sports compared to other countries.

Fast was on the mountain with six other speed flyers, two of whom made it down safely, said Carothers. The others encountered strong winds and had to break off, but Fast was last seen skiing down the mountain and taking off, she said. "In all the searching there hasn't been a shattered ski or a piece of nylon or anything in the area."

The family has enlisted the help of two U.S.-trained search and rescue experts and is using drones to fly over the dangerous terrain that includes a glacier with deep crevasses.

"We are very realistic about knowing that there is no way he is alive if that's where he did land because of the subarctic temperature," said Carothers. "But we're trying to do what we can do so we're focusing on the lower areas where if he did make it down there he would be alive."

The family has set up a fundraising appeal to help pay for the search that has already received over $50,000 in donations.

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Fundraising appeal: https://www.youcaring.com/harrison-fast-546235