How the heck do you contact (via letter) some who's a Billionaire or some entertainer like Britney Spears or Jay-Z?

How about William Wrigley Jr (the gum family) or Mark Cuban (Dallas Mavericks), they're involved in so many different businesses, where would I call or send a letter or have a courier deliver something?

Of course they have BIG gatekeepers but i figure if someone was creative enough it might get passed on.

Has any ever successfully contacted someone of this type of celebrity?

Thanks again!
Matt