Crews combed rugged terrain early Tuesday in the hopes of finding an 18-year-old autistic hiker who wandered away from his parents.

For a second night, temperatures dropped to around 40 degrees in the region where 18-year-old Jacob Allen is believed missing.

When he disappeared two days ago, Allen had no food or water with him. He was wearing a long-sleeved T-shirt, wind jacket, wind pants and hiking boots in the Dolly Sods Wilderness, said Chris Stadelman, the search group's spokesman.

Emergency responders and volunteers found his hat Monday, near where he had last been seen Sunday afternoon.

Search crews are focusing on 10 square miles of often rugged, steep and brush-covered terrain in the Randolph County section of the wilderness area, which is in the Monongahela National Forest.

"Some of it is back country where it's so thick you can't see five feet in front of you in the daylight," Stadelman said.

About 45 people searched overnight Monday, deliberately lighting campfires to make themselves visible in case Allen was nearby. More than 100 searchers were expected to help in the effort Tuesday, and dogs and helicopters also were being used.

Allen wandered ahead Sunday afternoon while hiking with his parents, Jim and Karen Allen of Morgantown. He didn't answer when they called his name, Stadelman said.

While Allen is described as severely autistic by his mother, Stadelman said, he is in good physical shape and likes to hike.