They started up the 23,000-foot Ogre-II peak in northern Pakistan on Aug. 21. The two were to reach the summit and descend in five days.
But two weeks later, the mountain climbers from Utah have yet to return.
The Alpine Club of Pakistan announced Thursday that Kyle Dempster and Scott Adamson, who arrived in Pakistan on July 24 for a two-month expedition, were missing in the Gilgit-Baltistan region, the Associated Press reported.
Spokesman Karrar Haidri said the club got in touch with local authorities and the climbers' families after they did not return on the expected date, the Associated Press reported.
Pakistani military helicopters will begin searching Saturday morning, Pakistan Standard Time, after weather conditions hampered rescue efforts for 10 days, Jonathan Thesenga, a friend of the climbers, told The Washington Post.
"It's a very difficult time right now because of the unknown and because we want to get up to them and help them," said Thesenga, who said he's been in contact with the search crew in Pakistan. "We owe a huge amount of gratitude to the Pakistani government for scrambling all of their available assets and their commitment to finding Scott and Kyle."
The climbers' family started a GoFundMe campaign Wednesday to help pay for the costs of the rescue efforts. In two days, more than 4,000 people have raised more than $173,000.
Dempster and Adamson were last seen Aug. 22, when their headlamps were spotted roughly halfway up the peak, according to the GoFundMe page. But a snowy storm moved in the next day and has continued in the region since.
Thesenga, of Utah-based Black Diamond Equipment that sponsors Dempster, said the two nearly died last year when they tried to climb the icy and treacherous Ogre-II peak, which rises from the Choktoi Glacier in Pakistan's Karakoram range in the Western Himalayas.
This year, they decided to return.
"They wanted to finish what they started and summit the peak," Thesenga told The Post.
Dempster, 33, and Adamson, 34, are two of their generation's most accomplished alpinists and have built their careers climbing some of the world's tallest peaks, Thesenga said.
After the unsuccessful attempt last year, Dempster wrote an essay about the climb published in the Adventure Journal:
“When people asked about my summer expedition to Pakistan, I found a myriad of ways in which I could answer. All were true, but some were substantially more brief than others. To family and friends I prefaced the complete experience with, ‘I'm really sorry. I nearly died. I could have killed Scott. It was my negligence, and I promise it won't happen again.’ I watched as their faces melted from excitement to concern to heartbreak. Tears were shed and I saw their trust in me evaporate."
“Fault in judgment and action call on the individual to own his or her mistake. I've apologized. I'm grateful to have learned. And because of that lesson, I'm now a safer climber. I count on seeing my future — all purpose is directed toward staying alive. After all, life is awfully fragile, and something as trivial as a tiny stick breaking in the woods can change its course.”
Earlier this year, two European climbers discovered the body of fellow climbers David Bridges and Alex Lowe, who vanished in a massive avalanche in 1999.
Hikers David Goettler and Ueli Steck found the remains while climbing Tibet's Shishapangma, the world's 14th-tallest peak, towering at about 26,000 feet above sea level.
Dempster and Adamson have known each other since they were teenagers and are frequent climbing partners, Thesenga said.
Dempster co-owns High Ground Coffee in Salt Lake City, according to a short biography on Black Diamond Equipment's website. He first started climbing in 1994.
His perfect day, he wrote, involved the smell of coffee waking him up before the sun rises.
"Crawl outside of a sleeping bag. Pack up camp. Climb into the night. Kiss my girlfriend and thank her for a great day. Repeat," Dempster wrote.
Adamson started climbing at age 16 and quickly became an active member of the climbing community in Utah.
"Scott's ultimate goals, even from a young age, are putting up long technical alpine mixed lines in the greater ranges; chasing the unknown," according to a short biography on the Liberty Mountain's website. "Over the past 20 years he has been filling the gaps to achieve that goal in all mediums of climbing."
Thesenga said the men's families remain optimistic that the two will be found.