I have yet to find a comprehensive list of which PR/UF/SCI-FI/SF/YA/Horror authors are on Twitter. You can find me here

Here is who I have found so far:

Karen Dales  Cynthia Eden Diana Rowland

Tate Hallaway Tracey O’Hara Anton Stout 

Jocelynn Drake JA Konrath Tom Upton

Nicole Peeler Kimberly Frost Keri Arthur

Angie Fox Laurell K. Hamilton Gena Showalter

Annette Blair Jeaniene Frost Rachel Caine

Kelley Armstrong Christina Dodd Jackie Kessler

Dianna Love Sherrilyn Kenyon Vicki Pettersson

Rachel Vincent Melissa Marr Caitlin Kittredge

Linda Wisdom Jaye Wells Mark Henry

Michelle Rowen Katie MacAlister Jenna Black

Candace Havens Adrian Phoenix Lilith Saincrow

Catherine Karp Chloe Neill Dakota Cassidy

Nalini Singh Marta Acosta Lara Adrian

Richelle Mead Michele Bardsley Kelly Meding

Maggie Stiefvater Christopher Moore Cassandra Clare

Holly Black Scott Westerfeld Jennifer Armintrout

L.A. Burton Jeri Smith-Ready Neil Gaiman

Sharon Ashwood Erin McCarthy Michele Hauf

Molly Harper Terri Garey Kathy Love

Annette McCleave CM Priest

As always, if I have missed someone, let me know!