How do I negotiate use of copyrighted characters?

I want to use a few copyrighted cartoon characters in a play I am writing. I would like to know how to do so. I have never dealt with requesting use of copyrighted characters before. Also if you know who now owns these characters that would help a lot. I wanted to use Yogi Bear, Boo-Boo (I think Hanna-Barbera is owned by fox now) Winnie the Pooh, and Smokey Bear.