When we can't hold public events in person, authors have to rely on online methods to hold book releases, publicize their older work, or otherwise keep themselves and their books in front of their fans and potential new readers. Joel Friedlander's The Book Designer website recently featured a couple articles to help you.
It's a Wide WIDE Virtual World! by Judith Briles
Author Blogging: 5 Reasons to Start and 3 Ways to Do It Right by Brandon Cornett (and you should be blogging anyway)