Upgrade to get full access to all premium news on Yahoo Finance and get more great articles like this free preview. Bill Ackman has told potential investors in the US-based investment fund he is working to take public that his prolific social media presence will help the vehicle trade at a premium valuation. The billionaire hedge fund manager is soliciting investments for a listed fund of up to $25bn called Pershing Square USA, which if successful, would make it one of the largest initial public offerings of all time, rivalling oil major Saudi Aramco (2223.SR) and Chinese tech group Alibaba...