Police on inflatable paddle boards have joined the police air wing and SES in the search for a man missing near the Yarra River in Melbourne's outer east.
Investigators have been told the 39-year-old man was with friends at Taroona Reserve, Warrandyte on Saturday when he walked down a path toward the river by himself about 3pm.
His worried friends later tried to find him before contacting police to report him missing.
The area is part of the Warrandyte State Forest. One side of the river is a popular walking track for locals and the other is covered by dense bushland.
Acting Sergeant Will Calleja was unable to questions about whether the man was a local or visiting the area.
He said a large search effort was underway with the air wing, police divers, foot patrols, boats and the SES taking part.
"We've searched an area of four kilometres across the river," Act Sgt Calleja told media at the scene.
Anyone with information is urged to contact Crime Stoppers on 1800 333 000.