Facebook’s stock has plunged to a new low today, now that one of the bans preventing insiders and early investors from selling their shares has expired. So far today, Facebook’s stock has plunged down to a low of $19.69, although it’s currently bounced back a bit and is trading at just over $20. This is close to 6% down from Wednesday’s close, and close to 50% below the price of its initial public offering, which was $38. This means that the stock has lost nearly half of its value since its IPO, which was one of the most anticipated in history. Some of the investors eligible to sell today are firms like Goldman Sachs and Microsoft, Zynga CEO Mark Pincus, and various Facebook board members. It’s unclear whether stock prices are declining because the marketplace is now flooded with their shares, or because other investors anticipated such an event. This is only the first of multiple lock-ups, which are meant to prevent volatility. 271 shares were freed up today, but another 247 million shares will be freed up on October 16th, and November 15th will see the unlocking of 1.2 billion shares.