Richard Johns, 52, set off alone on the hike from Halls Gap to Barooka Lookout in the Grampians National Park about 2pm yesterday and never returned.
Johns is not familiar with the area, Victoria Police said in a statement.
Police officers in the air, park rangers and the SES have been scouring the bush for any sign of the missing hiker.
The temperature is predicted to drop down to 1C tonight.
Johns was last seen wearing a blue zip up jacket & pants.
Police urge anyone with information on his whereabouts to contact Ararat Police Station on 53355 1500.