X's advertising revenues have dipped under Musk's leadership, and the acquisition has accrued $13 billion in debt. read more. : Renowned investor Bill Ackman could be planning an investment in X, the social media platform owned by Elon Musk, through his firm Pershing Square Holdings Ltd PSHZF. What Happened: According to The Wall Street Journal, Pershing Square obtained regulatory approval last Friday for a novel investment vehicle aimed at investing in a privately held company with the intention of taking it public.