When you find where Mike and Sulley are...if they are not there, go back later and check. We stumbled across their "home" and they were not there. There is a board out front that states when someone will be there taking pics, I believe..well, the sign was empty so we figured they weren't there that day. Well, we went back by about 1 hour later and they were there...and the sign had a whole bunch of times on it!!
Good Luck!!