31-year-old Joel Thomazin was last seen Monday, September 6th.
Someone reported seeing him on the trails around Hetch Hetchy.
Investigators say Thomazin planned on hiking from Hetch Hetchy to Lake Eleanor and back.
He should have finished the hike by Wednesday but hasn't been seen in more than a week.
Thomazin stands about five feet ten inches tall.
He has a yellow and gray backpack and an inflatable red kayak.
Anyone with information or who sees Thomazin is asked to call the National Park Service.