The search for a missing 11-year-old Boy Scout entered its third day Monday in Utah's rugged mountains, with police and volunteers using dogs, horses and all-terrain vehicles.

Thousands of volunteers have scoured nearly six square miles of the High Uintas (search), about 80 miles east of Salt Lake City, for Brennan Hawkins (search) of Bountiful, who was last seen Friday night at a Boy Scout camp.

"He's probably dehydrated, sleep-deprived, definitely hungry," said Brennan's father, Toby. "With him being so young at 11, I don't think he's thinking about what he needs to do to survive because he's never been in that environment."

Brennan was last seen near a climbing wall at the 8,500-foot elevation Scouting site, not far from the swollen East Fork of the Bear River (search).

About 3,000 volunteers searched for the boy on Sunday, when some churches in Brennan's hometown of bountiful, north of Salt Lake City, canceled services so their members could help.

Jody Hawkins she has sat in the campground the last two days, staring at hills wondering if that's where her son is lost. She said some of the volunteers were discouraged because they didn't find Brennan Sunday, but she assured them their help is valuable.

"I know where's he's not now, I know he's not in those hills," Jody Hawkins said. "We got that much closer because of those people."

Summit County Sheriff Dave Edmunds said searches of the rugged wilderness had turned up no evidence so far, but investigators remain hopeful that the boy is simply lost. Nonetheless, investigators were exploring the possibility of foul play, especially since there were quite a few people in the mountains.

"It's very important that we conduct a comprehensive investigation, and part of that is looking into possible criminal activity," Edmunds said. "We want to know who was in the woods up here."

A climbing-wall supervisor said he saw the boy about 5:30 p.m. Friday struggling to remove climbing gear. At the same time, he saw the boy's friend walking down a dirt road toward the family's campsite about 200 yards away. The supervisor looked away and then looked back, but didn't see either boy, said Chief Deputy Sheriff Dave Booth, the search and rescue coordinator.

Brennan, who recently completed the fifth grade, was wearing a blue sweat shirt, black shorts and white tennis shoes when he disappeared. Search officials were not concerned about exposure since temperatures have been warm, only reaching the 50s during the nights.

Brennan's mother said the boy had a lot of outdoor experience. His father said the boy is shy and might not approach a stranger to confess he is lost.

Authorities are fearful the boy may tried to cross the East Fork of the Bear River, which comes within about 50 yards of the camp. Two swift-water dive teams searched the river for miles on Sunday, and were setting out again on Monday.

"The biggest risk is the river," Booth said. "It's over a man's head in some places, and the current is swift."

The mountainous area being searched is just 15 miles from where 12-year-old Garrett Bardsley (search) vanished last summer while camping near Crystal Lake. Bardsley was never found, despite a wide, weeklong search.

Booth said the area of the current search is less severe than where Garrett was lost — not as high, steep or cold.

Bardsley's father, Kevin Bardsley, joined the search for Brennan, fulfilling a promise he made when ending the search for his own son.

"When we came off this mountain in the winter, my friends and I decided right then, if anyone came missing, we'd be there immediately," he said. "I never stop thinking about my son, and I never will the rest of my life."