A threat of rain combined with a third long night of freezing temperatures raised fears Monday night for the safety of a missing 12-year-old Boy Scout who vanished over the weekend in a heavily wooded mountain area of North Carolina.

Searchers, aided by a helicopter and dogs, fanned out around Doughton Park looking for clues to the whereabouts of Michael Auberry, who disappeared Saturday afternoon while on an overnight hiking trip with his Boy Scout troop.

Other than a mess kit, food wrappers and drawings in the dirt, searchers had no clues to the little boy's location, according to National Park Service spokeswoman Tina White. The FBI joined in the search Monday, issuing a missing person alert "just in case" Auberry had wandered out of the search area, she said.

"We have no clues or anything to indicate that there's foul play or anything involved in this at all," White added.

"I think we're still confident in calling it a search and rescue mission," White told reporters, adding that search operations would scale down during the night to include a few dog teams, some National Park Service and 15 state park rangers.

"They'll be using specialized equipment," she said. "There are advantages at night in the use of heat sensory equipment... if it gets down in the 20s and 30s tonight there will be a great big difference in body and air temperature," making it easier to spot Auberry, she said.

"Dog team owners advise that at night a scent can settle into low-lying areas because of dew," White said.

"We're very concerned," she added. "Every night is another night out in the cold ... even with all the clothing and gear I'm sure it's not a comfortable situation for him. We're very concerned."

White said Michael's parents were on the scene helping the search and that federal, state and local officials were aiding in the effort, as well. She said they all will continue the search so long as they're needed.

"I've got my long underwear on. We're prepared for the cold temperatures and are ready to work well into the night," White said. "He's had some scary nights out in the woods ... but I think the thing that makes me optimistic is his clothing … he's dressed really well for that [cold]. Although it's been really cold over the past few nights, it's still manageable."

Weather reports showed rain probable overnight, and searchers were nervous Auberry's clothes could get soaked while he tried to battle cold weather.

Some 70 ground searchers, a state police helicopter and five dog teams picked up the search for Michael, who wandered away from his troop's campsite along the Blue Ridge Parkway.

Chopper and tactical tracking teams joined ground searchers checking drainage ditches and crevasses. They were to focus their search in the area from where Auberry's mess kit was found and outward.

"The most probable thing is that he walked away, went out in the woods and went to investigate," said David Bauer, a ranger with the parkway.

Auberry, of Greensboro, has been a Scout for about a year and has a first-class rank, his father, Kent Auberry, told the Winston-Salem Journal. The Scout's parents said he likes to camp but doesn't like the cold.

A bright sun pushed temperatures Monday into the 50s. Boy Scout officials said part of the training Michael received was how to treat himself for hypothermia.

The rangers were working with the boy's family to learn everything they could about Michael's wilderness skills and how he might react to the situation.

Michael, who suffers from attention deficit hyperactive disorder (ADHD), last was seen wearing a red heavy outercoat and an inner fleece coat, and had gloves and a hat in a pocket. He was wearing a dark blue University of North Carolina Tar Heels baseball cap.

Auberry is 5 feet, 4 inches tall, weighs 110 pounds and has reddish-brown curly hair.

“He’s trained to seek shelter at night, cover himself up with leaves” for warmth, Bauer said. "We're hopeful at this point ... I've been on searches that have lasted over a week in worse weather and we've had successful outcomes.

"He was dressed appropriately for the time of year. It was going to be a miserable night for him, but survivable."

In such conditions, survival is possible for weeks if one is prepared, White said.

"The most important thing is for [Auberry] to stay in one place," she told FOX News.

White said is crucial the search because in "the area here, we have sort of a combination of mountainous terrain … but also some more piedmont area, too," and helicopters and other search-and-rescue aids are better equipped for daytime searches.

"Our biggest concern would be cliffs and dropoffs," she added.

Trails and fire roads, as well as rugged off-road areas were being looked at in the search, Bauer said.

About 10 scouts and their three adult leaders of Troop 230 noticed Auberry was missing after eating lunch together Saturday.

Bauer said Auberry stayed behind with an adult leader while the rest of the troop went for a hike Saturday "because apparently he wanted to sleep in." The troop members returned and ate lunch with Auberry and the leader. Soon after, between 12:30 p.m. and 1 p.m., they noticed Auberry was missing from the camp, he said.

Bauer said he's not aware of Auberry having any arguments or problems with the troop or his family.

Search crews have included volunteer firefighters, National Park Service staff and rescue squads from the state park system and Alleghany and Wilkes counties. A Highway Patrol helicopter equipped with an infrared sensor that can detect body heat was sent to assist the search.

Volunteer leaders are asking for help from area rescue squads and fire departments to aid the search. White said the number of volunteers had swelled to where the National Parks Service was planning to created teams of experienced and trained trackers.

The Associated Press contributed to this report.