Police believe they've found the body of a missing Melbourne man in a state park more than three weeks after he disappeared.

Yiwei Chu, 28, from Mount Waverley, was last seen buying lunch at a Hungry Jack's about midday on Wednesday, April 11.

His disappearance sparked a major police and SES search and an emotional public appeal for information from his family.

A passerby found a man's body in the Werribee Gorge near Ironbark Road about 6pm on Thursday.