You wouldn't see your tweets on the celebrity's main page (for example, http://twitter.com/aplusk).  Only the celebrity's own tweets show up there.  However, you can see a recent public message to the celebrity in a search for @celebrity (such as http://twitter.com/#search?q=@aplusk).  (You could add your user name to the search to find more of your messages.)  In this case, Ashton Kutcher could see your recent messages in his @aplusk sidebar, which is basically the same as your search on Twitter for @aplusk.