Hawaii County authorities had no luck Friday as they continued the search for a tour plane that went missing over the Big Island. Fire Department Battalion Chief Bob Bailey said he has not given up hope of finding the aircraft and the three people onboard despite the fact that no sign of it was found Friday.

"We're thinking positive, always," he said.

The Coast Guard helped in the search for the first three days, but did not join in the Friday effort.

Two county helicopters and four planes from Island Hoppers, the company that operated the lost plane, resumed the aerial search at daybreak Friday, covering some of the same ground that has already been searched.

The county plans to continue searching through the weekend.

The plane departed from Kona International Airport at 10:25 a.m. Tuesday for a three-hour tour but never returned. There was no distress signal or radio contact from the plane before it vanished, according to the Federal Aviation Administration.

Hawaii County Fire Chief Darryl Oliveira has said the aircraft was last spotted near Kilauea's eruption area and was believed to have been heading south to return to the airport.

The passengers aboard the plane were identified Thursday as Nobuhiro and Masako Suzuki, a couple from Urayasu, Japan.

The pilot of the single engine Cessna has been identified as Katsuhiro Takahashi, a senior pilot and chief flight instructor.

Crews from Civil Air Patrol accompanied by fire department personnel also searched by foot, going into interior areas of the Big Island that have undergrowth and trees so thick a downed aircraft may not be visible from the air.

Bailey, who has been with the county Fire Department since 1974, said he does not recall an instance of an aircraft vanishing and not being found.

"We want to find them," he said.