Mute Autistic Boy, 9, Missing in Virginia

DOSWELL, Va. Oct. 27, 2011— -- As near-freezing temperatures threatened to set in at nightfall, more than 1,000 volunteers spent today searching rugged Virginia woodlands for a 9-year-old autistic boy who has been missing since Sunday.

Carrying walking sticks and wearing yellow reflective jackets, the searchers began lining up before dawn to be taken to the forest where they were to look for Robert Wood, Jr.

"I have an 11 year old, and if the situation were reversed, I would hope people would be out helping me look for her," said a man named Don who stood in line for hours in the parking lot of an amusement park to take part in the effort to find the boy.

Hanover County sheriff's officers say Robert, who does not speak, ran off from his father while they were visiting North Anna Battlefield Park on Sunday.

After five days, the search has been fruitless. Some areas of the park have been covered by search teams at least twice. With weather forecasters predicting temperatures in the upper 30s early Friday morning, the effort took on new urgency today.

"We are not giving up," Hanover County Sheriff's Capt. Mike Trice said today. "Our mission is clear."

Trice acknowledges after several days of mild temperatures, it's going to be very cold in the woods early Friday morning.

"We are in a life-saving mode, definitely," Trice said.

Officials have broadened their search area to a 3.5 mile radius from where the boy was last seen, up from 2.5 miles. They have also stopped the flow of water into the North Anna River, to aid divers in their search of the water.

Specialized teams will use infrared, thermal-imaging and night vision technology as they continue looking for Robert overnight.

The number of searchers has also increased.

"They said they needed more volunteers today because time is of the essence," said Stephanie Saccone, a Richmond resident who had been watching news coverage of the search all week.

Eddie Buchanan, division chief of Hanover County Fire/EMS, told ABC News that so many volunteers showed up to look for Robert today that hundreds were sent home after receiving training, in the hopes they would return tomorrow.

No searcher goes into the field without receiving protective gear and being taught by an autism specialist how to interact with Robert, should they find him.

"It's so that they understand that in case they do get lucky and encounter him, how to handle that so they don't scare him or make things worse," Buchanan said.

"We know that he's quite a runner, he's quite a climber, quite a fast little guy," Buchanan said, but Robert's parents tell officials he won't respond when his name is called.

"It's such a rough terrain and such a rough situation," said Carrie Christ, a firefighter and paramedic who drove 60 miles from York County, about 60 miles east of Hanover, to take part in the search for a second straight day. "I don't know why they haven't found him. They're making every effort."

"We believe that Robbie's out there. We believe that he's alive," Buchanan told ABC News. "We're going to keep searching and doing everything we possibly can, for as long as we can, until they tell us to stop."

"You've got to be hopeful. You wouldn't be here if you weren't hopeful," said Christ.