In recent years, the secondary market for stocks – a platform through which investors can buy and trade shares of private companies – has grown exponentially in size and use.  This year,    transactions on the online platforms of SharesPost and SecondMarket alone have totaled over $ 4.6 billion, and are projected to exceed $ 6.9 billion next year. This does not include the much larger volume of trading by traditional broker-dealers and financial advisers, or other online platforms.