Heat-detecting cameras and sniffer dogs have been unable to give police any further clues into the whereabouts of a boy missing in dense Victorian bushland.

William Callaghan’s family has spent a second anxious night at Mount Disappointment, where temperatures again reached freezing point, as police and volunteers “race against time” to bring Will home.

The search will resume at first light on Wednesday and police are inviting volunteers with specific search and rescue skills, or detailed knowledge of the area, to help.

They said they had been “overwhelmed” by support, and thanked the community, but asked that volunteer numbers be managed given the low visibility and a need to keep rural roads clear for emergency vehicles.

Penny Callaghan says her 14-year-old non-verbal autistic son will be scared, hungry and cold after going missing wearing only a blue hoodie and track pants as temperatures plummeted to near-freezing on Mt Disappointment, north of Melbourne.

“Any parent, I’m sure would be thinking the worst-case scenario. I can’t do that at the moment. I’m really hoping that we find him today. I don’t want him out another night,” she told reporters at the scene.

Will, who has autism and does not speak, was last seen about 2.20 on Monday.

The 14-year-old had been walking to the summit of the hiking spot when he raced ahead of his family and became separated from them.

Will was wearing blue trackpants and a hoodie the day he disappeared, and there are grave concerns for his health in the cold environment.

“When you have someone out lost in the bush, we are fighting against time,” Search and Rescue Squad Senior Sergeant Greg Paul said.

More than 200 volunteers joined about 150 police and emergency services who have been looking for William non-stop while temperatures drop below zero.

William went missing without food and water and could have covered a lot of distance, police said.

It is believed he could have tried to walk into a house for food or put himself to bed, and police have asked neighbours to check their outhouses.

“William doesn’t verbalise so if anyone finds him, the best way to communicate with him is to be patient and calm,” Acting Inspector Christine Lalor said.

-with AAP