Complex sentence: To Halpern's surprise, the Twitter profile quickly gathered a large following--a friend posted a link to his feed, followed by Rob Corddry, and "that really jump-started it," according to Halpern.
Split into simpler sentences: To Halpern's surprise, the Twitter profile quickly gathered a large following. A friend posted a link to his feed; when Rob Corddry mentioned the page "that really jump-started it," according to Halpern.