Christos Pittas left for a planned 90 minute walk from Big Muster Drive at Dinner Plain about 2.45pm on Friday.

The Greensborough man, who had planned to spend a week on the mountain with his wife, was reported missing by her about four hours later.

Despite an intense search of the surrounding area, emergency services have been unable to find any sign of the nature enthusiast.

His daughter Elia Bird wrote on social media on Sunday night that time was against the family.

"We assume he got lost off of one of the many hiking trails and perhaps injured himself," she said.

"Tonight will be his third night out poorly dressed in the wild terrain.

"Time is against us with the snow coming in on Monday."

The temperature dropped to zero degrees on Monday, with an apparent temperature of -10.

Mr Pittas left without a phone or food.

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An intense search involving about 120 people, mostly volunteers, has focused on a three kilometre radius surrounding his last known location.

The search has mainly occurred during daylight hours but some have continued looking for Mr Pittas during the night.

Senior Sergeant Doug Incoll said the search wouldn't be possible without volunteers, which included his children, the SES, firefighters, and other agencies.

The terrain includes cliffs, gullies, creeks and thick undergrowth, and there are concerns the 70-year-old may have gone away from the defined trails.

"Police are still hopeful of a successful outcome but as time goes on, it's more concerning," he said.

"The majority of people here are volunteers and this wouldn't be achievable without their assistance."

The police air wing, mounted branch, public order members, search and rescue squad and general duties officers have been involved.

Visibility has dropped at times to 50 metres.

Senior Sergeant Incoll urged people in the high country to be prepared with food, water, a map, appropriate clothing and emergency location beacons.

Anyone with information can call (03) 5723 0888 or 1800 333 000.

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