Legislators on both sides of the Atlantic have given Facebook boss Mark Zuckerberg a stark message: you need to tell us why you let Cambridge Analytica harvest data from tens of millions of Facebook users. And you need to do it in person. Not just lawyers. Not spokespeople. You, Mr Zuckerberg. The demands came as the tech giant’s share value continued to plummet, with almost $50 billion wiped off its share price.