But for the vast majority, a fan (or a convention chair, or a potential agent from outside the industry) would need to go to the publisher of one of their books to contact an author. Practice, and chats with some of the desk workers at publishers, led me to recommend a three-envelope system for making this contact.
On the outside, there's the one that gets addressed to the publisher. The address from the indicia page on the most recent book is usually a good starting spot.
Inside that is a note to the publisher, explaining who you are, why you would like to contact the author, and asking for their help in getting the enclosed envelope forwarded.
There is also the second envelope, already sealed, (here's the important part) already with the correct postage on it, and with just the author's name in the "Send to" area. This lets the publisher either dump the envelope in with the gathering pile of things that will eventually be wrapped up and forwarded to the author OR (maybe, you hope) since the postage is already on it, have the address scrawled in and the letter dropped off in the mail. Could go either way really, but you up your chances.
Inside the sealed envelope is your (professional, polite, spellchecked) letter to the author and -envelope number three- a self address stamped envelope for their reply (if any).
Even today, if I was not able to contact someone by email, the envelope system would be worth a try, and should always include an SASE. Even when they are likely to email me back, sending a printed letter means that I include a way to send a printed letter back. Not everyone spends all their time on the internet. (No, really, it's true!)