Sir Richard Branson has backed missing adventurer Steve Fossett to return safe and well.
The 63-year-old world aviation record holder was last seen taking off from the Hilton Ranch south of Smith Valley, Nevada, on Monday night in a single-engined aircraft.
It is believed Mr Fossett was searching for empty and dry lake beds which may be suitable for a forthcoming world land speed record attempt in a car.
His adventures have been financed by entrepreneur Sir Richard, who said: "Steve is a tough old boot.
"I suspect he is waiting by his plane right now for someone to pick him up.
"The ranch he took off from covers a huge area and Steve has had far tougher challenges to overcome in the past. Based on his track record, I feel confident we'll get some good news soon."
The American millionaire businessman who holds the record for flying further than anyone in history, was the first person to fly solo around the world in a balloon, and the first person to fly a plane solo around the world without refuelling.
Teams were searching hundreds of square miles of rugged terrain in western Nevada for the adventurer.
Mr Fossett took off at around 9am local time on Monday from a private airstrip on a ranch south of Smith Valley in western Nevada.
When he did not return by noon as scheduled, a friend reported him missing.
Virgin tycoon Sir Richard later told BBC News 24 that Mr Fossett had a special watch which, if he was able to, he could use to give out a signal to show his location. But he had not done so.
He said: "Steve has been through some near misses and he has always come back alive and well...
"Everyone is concerned, but our hope is that he will turn up in the morning alive and well somewhere in America."
He described Mr Fossett as a "remarkable individual", who is calm, with a great sense of humour.
He added: "There is nobody on earth like him."
He said Mr Fossett calculated all his adventures carefully. "I am hopeful that he will be found alive."
A spokesman for Sir Richard added that Mr Fossett was flying solo with two full tanks of gas on the plane.
Fourteen aeroplanes, along with ground crews, are involved in the search.
The aircraft, with the tail number N-240R, is blue and white with orange stripes and blue sunburst designs on top of the wings.
US federal aviation administration spokesman Ian Gregor, said: "The Civil Air Patrol is looking for him. One problem is he doesn't appear to have filed a flight plan.
"They are working on some leads, but they don't know where he is right now."
It is understood he would have had four to five hours of fuel in the plane and was not wearing a parachute.
A Civil Air Patrol spokeswoman said it was "just a little out and back excursion" and Mr Fossett had "more than enough fuel on board" .
She said conditions were "optimal" on Monday, with more than 10 miles of visibility, with light winds. Heavier winds yesterday were hampering the search.
"As far as we know now, it's still a rescue mission," she said. "Until we have more information, it'll remain that."
She added that it was common practice not to file a flight plan when using a private air field, "especially if you don't plan on being gone very long ".
Mr Fossett took off from a private airstrip at a ranch owned by hotel tycoon Barron Hilton.
Last year, Mr Fossett smashed the record for flying further than anyone in history.
His record journey was sponsored by Sir Richard, who is also known for his daredevil record attempts and followed Mr Fossett in a support plane.
In March 2005, he became the first person to fly a plane solo around the world without refuelling.
And in 2002, Mr Fossett was the first person to fly around the world alone in a balloon.
The 63-year-old has also climbed some of the world's tallest peaks, including the Matterhorn in Switzerland and Mount Kilimanjaro in Tanzania.
He swam the English Channel in 1985, was placed 47th in the Iditarod dog sled race in 1992 and participated in the 24 Hours of Le Mans car race in 1996.
In 1995, Mr Fossett became the first person to fly solo across the Pacific Ocean in a balloon, landing in Leader, Saskatchewan, Canada.
Sir Richard paid tribute to Mr Fossett again in an interview with Sky News.
Asked to describe the adventurer, he said: "He is an absolute delight. We were in a balloon capsule together for 13, 14 days and he could not have been more pleasurable to be with.
"He is cool, he is calm, he has a great sense of humour, and you know you are in a safe pair of hands.
"If you wanted to get some sleep you could not have a better person at the controls.
"He is just an exceptional individual all round."Reuse content