Searchers looking for missing adventurer Steve Fossett have discovered half a dozen other plane crashes, but have found no substantial clues about the multi-millionaire's whereabouts.

Teams have been looking for Fossett for five days since he was reported missing on Monday.

The search is complicated by the fact Fossett, 63, filed no flight plan and told no one where he was heading when he took off in a single-engine plane Monday from a private airstrip 120 kilometres southeast of Reno, Nevada.

The search area has now been expanded from 26,000 to 44,000 square kilometres, and 45 planes and helicopters are involved.

It is akin to searching a rugged, remote area roughly half the size of Nova Scotia.

On Friday, hopes that a wrecked plane spotted on the side of a hill might be the plane Fossett was flying, were dashed. Ground crews reached the aircraft and reported it was last registered more than 30 years ago.

At the end of a discouraging week, Civil Air Patrol Maj. Cynthia Ryan said searchers are discovering "lots of stuff we didn't know was there."

She said authorities had received hundreds of tips from the public, but were focusing on four leads from residents of an area near the Nevada-California border.

She said search crews have a "pretty good handle" on at least half the search area.

Fossett was believed to be flying in the region, scouting dry lake beds for potential locations for a planned attempt to break the land speed record in a rocket-propelled car.

The thrill-seeker who made his fortune as a commodities trader has chalked up numerous such records in recent years and is probably best known for setting five world records for non-stop circumnavigations of the globe.

He achieved the records using hot-air balloons, airplanes, gliders and sailboats.

Following are some of Fossett's aviation accomplishments:

• 1998/2002: Long distance record for solo hot-air ballooning

• 2001/2002: Duration record for solo hot-air ballooning

• 2002: First solo balloon flight around the world

• 2005: First solo nonstop and non-refueled circumnavigation of the world in a single engine jet airplane

• 2002: One of aviation's highest awards: the Gold Medal of the Federation Aeronatutique Internationale

• 2004: fastest sailing circumnavigation of the world

• Ten of 21 Glider Open awards