It's been eight days since Riley Zickel was last seen before he disappeared into the Mount Jefferson Wilderness, and five days since search and rescue crews began to look for him. On Thursday, nearly 24 hours into his shift, Bob Lemke is staying optimistic.

Lemke, a search and rescue volunteer from Stayton, has been tasked with standing watch over Zickel's car, which was found on Saturday night near a Pacific Crest trailhead. It's still one of the only clues investigators have about Zickel's whereabouts.

Riley Zickel

Lemke is waiting by the silver Mazda just in case Zickel returns to it. It's nearing 4 p.m. and 90 degrees at the trailhead. Lemke's been stationed there since 3 p.m. the day before, watching the car and asking hikers if they have seen Zickel.

He's had no luck.

"Nobody's seen or heard anything," Lemke said. He paused. "We're still holding out hope though."

It's unusual for hikers to go missing for so long -- most searches are over in 24 hours or less. Zickel, a 21-year-old Lewis & Clark student from California, told family he planned to stay overnight in the Jefferson Wilderness on July 27. But authorities remain optimistic.

"He's young, he's healthy, he's experienced," Marion County Sheriff's Office spokesman Lt. Chris Baldridge said. "Our hopes are still high that we will be able to find him and return him safe and well to his family."

Zickel is an experienced hiker, according to the sheriff's office. He was carrying at least four days' worth of food, a water filtration device and other outdoor equipment, Baldridge said.

The lack of clues to Zickel's whereabouts, though, makes this search difficult. The only leads that authorities have are Zickel's car and one reported sighting on July 27, when another hiker spoke to Zickel in Jefferson Park.

Authorities thought they might have another clue on Wednesday when a photo taken by another hiker appeared to show Zickel standing near a tent at Sprague Lake. However, early Thursday morning, another hiker told deputies that the photo was of him, not Zickel.

The search and rescue crews are working with what they have, though. On Thursday, approximately 40 volunteers broke into teams and searched side trails north and south of Park Butte.

Before that, they scoured the area around Zickel's car, searched all of Mount Jefferson and an area called Park Butte. They've searched from dawn till dusk, on foot and on horseback. Investigators have tried to "ping" Zickel's cellphone and searched his browsing history and hiking chatrooms.

"If you can think of it, we've done it," Baldridge said. "We've done everything we can searching for clues."

Authorities have received other tips, but could not confirm any of them, Baldridge said.

Agencies from across the state have sent search and rescue teams to help find Zickel. On Thursday afternoon, a team from Multnomah County came straight from another search mission that started around 4:30 a.m. They plan to stay in Jefferson Park until dark searching for Zickel. After all, they have a lot of ground to cover. Their assigned search area is 104 acres, and they are trying to cover as much of it as possible before the day's end.

Other agencies' help has been invaluable in the search for Zickel, Baldridge said.

"It's powerful, when you have that many people volunteer their time and resources to help find another person," he said.

The crews don't have a time frame for the search, Baldridge said. They don't plan to stop any time soon.

"We'll search until we're confident we've searched every area that he could possibly be," he said.

Lemke has been part of the effort since it began on Saturday night, when Zickel was reported missing. On Thursday, as he watches Zickel's car, he occupies himself by looking at maps on the computer in his car or chatting with others on his ham radio. The only sound is buzzing flies and the occasional crunch of a hiker's boots against the gravel.

Soon, another person will take his place to keep watch over the car. Lemke will head back to the search and rescue's headquarters in nearby Detroit, eat dinner and rest. Then he'll go back out, to help search wherever he's needed.

In the meantime, though, he keeps watching the car.

"I keep waiting to see him bounce out of the woods and into his rig," Lemke said.

-- Samantha Matsumoto

smatsumoto@oregonian.com, @SMatsumoto55

503-294-4001