Can't find my Clownfish!!!!?

I can't find my clownfish and I don't know what to do. He seemed perfectly fine even yesterday. The only sign was he was closing his mouth like chattering it seemed like as if he had hypothermia. The water is like 77 degrees though. I searched everywhere around the tank, the outside, in the filter, and lifted to search under all my live rock. What do I do? Should I presume that it is dead?