Major brands engage Twitter by Chris Trayhorn, Publisher of mThink Blue Book, March 9, 2009 Customer engagement is a key social media metric and one that big brands are realizing can add a lot of value to their marketing campaigns. Here is a great rundown of 10 of the biggest brands using Twitter to reach and engage their customers – from HR Block to WholeFoods. Filed under: Revenue About the Author Chris Trayhorn, Publisher of mThink Blue Book Chris Trayhorn is the Chairman of the Performance Marketing Industry Blue Ribbon Panel and the CEO of mThink.com, a leading online and content marketing agency. He has founded four successful marketing companies in London and San Francisco in the last 15 years, and is currently the founder and publisher of Revenue+Performance magazine, the magazine of the performance marketing industry since 2002.