Update, 6pm: A quad biker who was missing in Sawyers Valley for three days has been found alive this afternoon.
Search crews in the area who were tracking his movements through bushland found Paul Pyke at about 4pm. He was severely dehydrated but was conscious and able to speak with police officers from the tactical response group.
The officers Mr Pyke emergency first aid and he was airlifted to Royal Perth Hospital in the RAC rescue helicopter, where he arrived at about 6pm.
Paul Pyke's quad bike was found earlier today outside the 300sqkm search area emergency services have been looking inside during the past two days.
Inspector Stephen Byrne said "quite substantial footprints" were also found today by State Emergency Service volunteers tracking away from the bike on Yarra Road.
The footprints prompted police to call in the tactical response group tracking team to replace volunteer searchers.
The group of four officers spent several hours following the prints in the hope of finding Mr Pyke.
Inspector Byrne said earlier today it was important Mr Pyke was found today as concerns grow for his ability to survive the 40C conditions without food or water.
"It is now crucial, it is now critical (we find him)," he said.
The search entered its third day today.
Mr Pyke, 35, was riding with two friends when he disappeared about 10am on tracks off Gorrie Road in Sawyers Valley.
The search continued throughout the night and intensified again this morning at first light. The polie helicopter was part of the overnight search, using a heat sensing camera.
Mounted police officers scoured creek beds this morning.
It was Mr Pyke's first time riding in the area. Friend Steven Madaschi believed it was easy to get lost in the maze of gravel and red dirt tracks that crisscrossed the dense bush.
"He must have taken the wrong turn and we just couldn't find him," Mr Madaschi said.
They searched for several hours before calling police about 1.15pm.
As each hour passed yesterday without any sign of Mr Pyke or the blue quad bike he was riding, concern for his welfare grew.
Police in the air and in vehicles, plus about 50 State Emergency Service volunteers, are combing a 50km-radius of bush and say the big distances Mr Pyke could have travelled make finding him difficult. Water, food, a flare, a torch and a note telling him to wait have been left on the car where he began the ride.
Mr Madaschi said he believed Mr Pyke was strong and could survive.