n. An intern hired to monitor and post messages to a company's social media accounts.
Other Forms
You know all of those unpaid work experience kids that are handed the keys of a business’ Twitter account? They now have a name for their situation — 'twinternship.’
—Oliver Milman, “The business buzzwords set to dominate 2013,” StartupSmart, January 22, 2013
A twintern is a graduate or university student who completes an internship at a company and has a focus on social media, including — but not restricted to — Facebook and Twitter.
—Cara Jenkins, “Interns help firms turn on social media,” The Advertiser, January 08, 2011
2009 (earliest)
COMPANY Pizza Hut Inc.

JOB TITLE Summer Twintern

JOB TITLE, TRANSLATED A summer intern who uses Twitter….

JOB PURPOSE …The Twintern must also play social-media defense, monitoring Twitter for any mentions of the brand and alerting superiors whenever anything negative about the Hut is being said.
—Stephanie Clifford, “Tweeting Becomes a Summer Job Opportunity,” The New York Times, April 19, 2009