Goodbye, Comcast Twitter guy.

Frank Eliason, the social-media apostle who responded to tens of thousands of online Comcast Corp. customer complaints in the last two years, is leaving the cable company to help banking giant Citigroup Inc. connect with customers online.

Eliason’s new title is senior vice president in New York, a sweet one for a 37-year-old who began his career stocking shelves in a  former discount chain, in the late 1980s.

Thursday is Eliason’s last day at Comcast. He chatted with Chief Executive Brian L. Roberts Wednesday morning — not the typical departure from a company with 100,000 employees — and then a grateful public relations department threw him a party.

Wrote Roberts in an e-mail: “Frank has had a huge impact on Comcast. He literally made himself available to our customers 24 hours a day, and he created a team of people who are dedicated to do the same thing.”

In the depths of Comcast’s customer-service woes, a time when an elderly Virginia woman busted up a Comcast office with a hammer because her phone had died and a blogger launched the Web site Comcastmustdie, Eliason began combing the Internet for Comcast references and responding to online rants. He found many of those on Twitter, the quick-blurb social-media site.

Eliason hit the Twitter moment almost perfectly. One business news story about Eliason and his tweets led to another and so on. Soon, people were talking about Comcast’s innovative use of social media to improve customer service, instead of about Comcast’s customer-service fiascoes.

Eliason’s department expanded from himself to 10 employees. Eliason, who has 42,000 followers on Twitter, said the Comcast digital-media group would continue tweeting.