A massive search in Big Cottonwood Canyon Wednesday failed to find any evidence of a Denver physician believed missing in the canyon since Sunday.

Salt Lake County Sheriff's search and rescue teams resumed the efforts to find Dr. Jake Gradwohl, 30, early Thursday morning.Gradwohl, a third-year resident at University Hospital, was last seen by friends on Sunday.

Tuesday afternoon, Gradwohl's car was located near a trail head about six miles up Big Cottonwood Canyon.

Some 50 searchers aided by teams from Rocky Mountain Rescue Dogs have been concentrating search efforts near Mill B trail.

Officials believe Gradwohl was lightly dressed when he disappeared Sunday.