How do you contact an author these days? There are a few I’d like to thank, but I have tried before and just given up finding a way to send them fan mail. Is there a place to easily contact many different authors?

I must have 300 characters to post so here is the title again: How do you contact an author these days? There are a few I'd like to thank, but I have tried before and just given up finding a way to send them fan mail. Is there a place to easily contact many different authors?

Specifically, I am looking to contact Ms. Rita Mae Brown author of Rubyfruit Jungle, and many others.