Caleb Forbes, 22, and Shannon Lowden, 21, set off on a camping trip near the Thomson Dam in West Gippsland on Friday but did not say when they would return.

The alarm was raised when Mr Forbes failed to turn up to work on Sunday.

Efforts to find the duo ramped up on Wednesday, with about 30 friends and family of the duo joining dozens of police, SES members and locals to search bushland around the Rawson, Aberfeldy and Thomson Dam areas.

Shannon's mother Debbie Lowden remains hopeful she will find her daughter alive and well.

"I feel like they've obviously got stuck somewhere and they can't get out," she told reporters.

"We will be here as long as we need to be here. We will be here until we find them."

She wanted her daughter to know she loved her and that there were fresh chocolate muffins waiting for her at home.

Police are yet to locate Mr Forbes' green 1994 Nissan Patrol wagon and believe it may have bogged or broken down in bad weather.

Inspector Shane Cashman said the search will continue to expand until police find the couple and the car.

"It's a search of over a thousand square kilometres that we have to cover and we're widening it as we go through and clear areas," he said.

The search for the duo, from Melbourne's northern suburbs, will continue on Thursday.

Australian Associated Press