March 18 (Bloomberg)-- The season-four finale of 'Pretty Little Liars' airs tonight. The show has been a ratings hit for ABC Family -- in part, because of its wild storylines. But also because of its big social media following, which includes more than two million Twitter followers. Showrunner Marlene King is a big Twitter user herself and even hosts "tweet parties" when the show airs. She speaks with Bloomberg's Jon Erlichman.