DRY FORK, W.Va. -- The brother and sister of a missing autistic hiker expressed hope this morning that their brother would respond to rescuers if spotted in the dense forests of West Virginia's Dolly Sods Wilderness Area.

Jacob Allen, 18, of Morgantown, W.Va., wandered away from his parents on a hike Sunday afternoon.

"He's very friendly. He loves people," said his 22-year-old sister, Brittany, a graduate student in Boston who flew in yesterday to help with the rescue effort. "If he sees someone, he'll be OK."

The search is complicated, however, by the fact that Mr. Allen is essentially nonverbal and cannot call out to rescuers. Described by his mother as severely autistic, "Mr. Allen has the mental capabilities of a 3- or 4-year-old child," said Chris Stadelman, public information officer at the rescue command center.

Hundreds of people lined up this morning in pre-dawn darkness to join the search for Mr. Allen. More than 200 volunteers combed a 10-square-mile area yesterday near the trail where Mr. Allen disappeared. An overnight search using about a dozen trained professionals and rescue dogs yielded several scents that rescuers plan to check today.

Officials said today that tracking dogs picked up dozens of scents overnight and searchers would be sent to those areas today.

Mr. Allen's 14-year-old brother, Micah, described the rough terrain in the search area.

"It's very steep and overgrown," he said, "If he wandered off, he could be five feet away and you wouldn't be able to see him at all."

Despite rain elsewhere in the state, the Dolly Sods area stayed dry overnight, with temperatures in the upper 30s and lower 40s. It is important, rescuers say, for the missing man to stay dry so he doesn't succumb to hypothermia.

Robert DeSantis, principal of Morgantown High School, where Mr. Allen is a senior, said that students yesterday morning made impromptu requests of fellow students for donations to help the searchers buy supplies.

"Within a couple of hours, the students collected $1,000 out of their pockets," he said.

He said that a couple of students who had survival training have been excused from school to participate in the search.

He said teachers requested a counselor to meet with students who have classes with Mr. Allen.

He said the school is "just anxiously waiting by to hopefully hear some good news."

More details in tomorrow's Pittsburgh Post-Gazette.