Victoria Police say a family has sighted a boy matching the description of missing child Luke Shambrook, who was last seen on Friday near Lake Eildon.

Reports say the family was driving near Devils River when they saw a boy that looked like the 11-year-old who has autism.

Searchers are now heading by four-wheel-drive to the area of the sighting, which is in rough terrain in Fraser National Park.

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“A family that was driving in the Devils River area have told police that they saw someone matching Luke’s description,” a Victoria Police spokeswoman told AAP late on Sunday.

“So they have extended the search to cover that area this evening.”

More than 120 volunteers and campers joined a large-scale emergency services search and rescue team scouring bushland at Fraser National Park near Lake Eildon.

More than 100 people, including dozens of campers, are searching Luke. Photo: ABC

Victoria Police Senior Sergeant Ralph Willingham said he had never experienced such an outpouring of practical support.

“We’re learning as we go, it’s certainly a new experience for myself the level of commitment, the level that people have put themselves to it today,” he said.

“We’ve got a system going, Victoria Police and the SES are actually nominating areas to be searched and recording what’s been done and who’s done it.”

“Some of those volunteers are on boats and jet-skis on the lake itself, searching the shoreline.

“We’ve got volunteers on motorbikes, on pushbikes and the majority on foot.”

Previously, Sen Sgt Willingham said Luke’s family and Victoria Police were still positive the young boy could be found alive and well.

“The advice I’m getting from our search and rescue experts, having regard to the overnight temperatures and daytime temperatures is that he could still be out there,” he said.

“We’ve got to be realist, but we’re positive and the family’s positive that if there’s any possibility, we’re comfortable that he’s still alive, that’s what we’re working towards and that’s what our efforts are focused on.”

Luke’s parents, Tim and Rachel, were receiving support from their family, extended family and church group, Sen Sgt Willingham said.

He became emotional as he read out the family’s statement of thanks.

“On this Easter Sunday, we are grateful for everyone’s compassion and caring, thank you for the special effort and huge support in trying to locate our son. We just want our dear son Luke found,” the statement read.

The weather bureau said conditions overnight were favourable to Luke, with a minimum temperature of 12 degrees at 6:30am (AEDT).

Park rangers search tents, cars

Earlier on Sunday police sent Parks Victoria rangers to search campers’ cars and tents for any signs of Luke.

“One of the things with Luke is that he enjoys watching DVDs and because of his autism he is willing to enter vehicles that have DVD players, and he doesn’t see anything wrong in what he does, it’s just part of his condition,” Sen Sgt Willingham said.

“We were just wanting to be reassured that he hadn’t got into someone’s car to do that … you can access vehicle boots from inside cars, so we just wanted to be reassured.”

Luke’s autism has been a challenge for rescuers, as hew may not know he is lost, police said.

“This is the problem; unfortunately Luke, with the autistic condition, he might not respond to searchers, he may not even know that he’s lost,” Sgt Greg Paul said on Saturday.

“He won’t necessarily respond to his name being called, but that might change a little bit as he gets hungry maybe.

“We honestly don’t know what his status is, whether he’s curled up sleeping somewhere, or hiding or whether he would necessarily respond to us looking for him.”

Family friend Stefan Van Rhyn said that when he first met Luke, he could talk a bit but had since “gone down hill”.

“I know that he doesn’t talk and he’s probably not in a good spot as any kid would be,” he said.

Sen Sgt Willingham said police did not believe Luke had been the victim of foul play.

“We’re considering everything that we can think of but our thoughts at this stage are that it’s a young boy that’s wandered off from the campsite,” he said.

“We can’t dispel every possibility, but whilst we’re considering it, it’s not one of our active lines of enquiry.”

Luke Shambrook, 11, went missing from the Candlebark Campground on Friday. Photo: ABC