LinkedIn Corp's shares plunged as much as 43pc on Friday, wiping out nearly $11 billion of market value, after the social network for professionals shocked Wall Street with a revenue forecast that fell far short of expectations. The stock sank to a three-year low of $109.50, registering its sharpest decline since the company's high-profile public listing in 2011. At least seven brokerages downgraded the stock from "buy" to "hold" or their equivalents, saying the company's lofty val...