lol, I had the same thing happen about 3 weeks ago. I finaly got my one clown to pair up with a tiny clown. Well one night I noticed the two were fighting, but didnt think anything about it. Clowns fight all the time untill they pair up. Well the next day the little guy was gone. I looked everywere. I even tore apart the tank and almost lost my anemone to a rock falling on it. About a week later I was unpluging some wires from my 55 gallon and the clown was a clown chip stuck to the wire behinde the 55. It made me feel better knowing it was not poluting the tank, but it is sad because this was the only clown out of 3 that my female liked

. Good luck finding yours, look under wires, and even in the HOB filter if you have one. They are good jumpers when they are being chased, lol.
Michael