A squadron of planes and helicopters resumed operations over a 600-square-mile (155,000-hectare) region of mountain terrain after failing to find any trace of Fossett during searches late Monday and Tuesday.
Fossett -- who has survived numerous brushes with death during a series of record-breaking solo flights around the world by balloon and airplane -- has not been heard from since taking off from a private airstrip early Monday.
Officials have described the task of locating 63-year-old Fossett's possible whereabouts as "like searching for a needle in a haystack."
Rescue planes were boosted by clear skies and calm flying conditions on Wednesday after being buffeted by turbulence during searches earlier this week.
Major Cynthia Ryan of the Civil Air Patrol revealed that high-tech hyperspectral imaging equipment known as ARCHER, which is capable of distinguishing between objects on the ground, had also been deployed.
"ARCHER is essentially something used by the geosciences," Ryan said. "It's pretty sophisticated stuff ... beyond what the human eye can generally see."
Later Wednesday Ryan revealed that rescuers had believed they had found Ryan's plane after spotting wreckage, only to be disappointed when it turned out that the debris was from an old crash site.
"We thought we had it nailed," Ryan said. "Unfortunately, it turned out to be one of many dozen unmapped wreck sites from previous years.
"We sent the helicopters there and they verified it was not Mr Fossett nor his aircraft."
Fossett was reported missing on Monday after he failed to return from a solo flight in a single-engine Bellanca plane following take-off from an airfield owned by hotel magnate Barron Hilton.
His aircraft was equipped with an electronic tracking device designed to be activated in the event of a crash but it had not been deployed.
Fossett made the first solo nonstop, non-refueled circumnavigation of the world in 67 hours in the Virgin Atlantic GlobalFlyer. In 2002, he was the first person to fly solo around the world in a balloon.
British tycoon Richard Branson, who partnered Fossett on earlier attempts to circle the globe in a balloon, said he had contacted Internet search giants Google to help with the search.
"I'm talking with friends at Google about seeing whether we can look at satellite images over the last four days to see whether they can see which direction he might have been flying and whether they can see any disturbances anywhere that they can pin from space," Branson told Canadian media.
The British billionaire said although he was concerned at Fossett's failure to activate an emergency tracking beacon, he remained positive.
"(Steve's) not only the greatest aviator in the world, he's also the greatest gliding pilot in the world," Branson said.
"I'm very confident that he would have got the plane down in one piece as long as the terrain below him was desert and not mountainous hills or woods or rocks.
"Having said that, obviously we're worried (about) the fact that there's been no emergency beacon go off. He could be injured, which means the emergency services have just got to get to him as soon as possible."
A multi-millionaire who made his fortune dealing stocks in Chicago, Fossett has spent the past two decades chasing world records and shattering them, sailing, floating and flying faster and farther than anyone before.
In 2006, he touched his aircraft down at an airfield on Britain's south coast, setting the record for the longest solo, non-stop, non-refueled flight in terms of distance.
Fossett has also set dozens of world records in sailboats, gliders and hot-air balloons.
"If you look at the history of adventurers, it is so often the simple things (that cause trouble)," Branson noted.
"Lawrence of Arabia went through everything and was then killed in a motorbike accident when he'd given up all his dangerous pursuits in Arabia. Anyway, I still feel confident that Steve will come back."