Officials said the friends searched for her all night and reported her missing Sunday morning.
"With the water being chocolate brown it's really difficult to find it. You can't see, the visibility is zero. We had some divers in the water yesterday and you can't see anything," said Lt. Steve Brown of Sonoma County Sheriff's Dept.
Crews are concentrating on an area where tire tracks were seen off Highway 1, as well as an oil and gasoline sheen in the water below.
