I have never seen Mike, but Sully appears frequently for M & G's in the Hollywood area in DCA. There is a section closer to the Monsters ride that is decorated like Monsters University. He'll be out there. My 2 year old son is pretty much afraid of all costumes characters. Sully is the only one I've seen him really excited to see. He went right up and gave him a hug.
I laugh when I think about how the monster he's not afraid of, but Cinderella...terrifying apparently.