The powerhouse social networking site, Facebook, still isn’t a publicly traded company; however, this doesn’t stop interested individuals from trading in its shares. In the past, movement of private shares has been largely opaque, but recently the advent of buyer-seller matching services such as SecondMarket and SharesPost, a little bit more insight can be gained into this activity.

And it’s become extremely active.

Social networking sites like Facebook, Twitter, and Linked In, and Zynga have increasingly become the center of a storm of private share trading—being the currently most sought after in the market. The Wall Street Journal has a lengthy article on the subject, but there’s a few interesting tidbits that might catch your eye,

Trading in shares of Facebook has been particularly strong in the past month. The surge began after a big transaction in November, when venture-capital firm Accel Partners, an early backer of the social-networking firm, sold less than 15% of its stake for $517 million, say people familiar with the deal. The deal, some details of which were reported on tech blogs, valued Facebook at around $35 billion, those people say.

Soon after the sale, Facebook’s trading volume and price surged on SharesPost and SecondMarket, two exchanges that allow trading of closely held firms’ shares. In the past month, the average valuation of Facebook based on transactions on SharesPost has risen almost 25%, to more than $56 billion, the exchange said. SecondMarket said Facebook’s valuation had risen about 12% over the same month. Such differences are possible because these aren’t public markets.

Facebook has announced that they don’t intend to go IPO until 2012, but that hasn’t stopped a lot of interest in the company to intensify the trade in their shares as investors prepare for that eventual day. While the trading itself and the increased valuation likely make investors and the social media company happy, it does raise concerns of catching the attention of the Securities and Exchange Commission, who regulate such transactions.

As a privately traded company, Facebook gains a certain opacity from the market that is in turn protected by their agreement to keep their stock trading on a tight rein. In 2007, Facebook took steps to curtail private trading by ceasing to offer stocks to new employees, instead giving them restricted bonds that would become stock at IPO. All this in an attempt to slow down the momentum of the private stock trading to retain their private status—if their total owners exceeds 500 or trading becomes too vigorous, the SEC may require them to reveal a lot more financial information.

And thus develops the primary and important difference between privately traded and publicly traded corporations which is the revelation of financial health to the market. Some analysis and market traders have been leery of this new behavior due to the fact that while it seems that Facebook is doing extremely well, it’s difficult to tell. The risk is might higher with private shares, because a company could be on the verge of losing market capability and shareholders wouldn’t know.

Although, such concerns seem a bit premature, especially when Facebook appears to dominate the social networking scene, manages to provide elaborate advertising capability to millions of customers a day, and continues to grow in leaps and bounds. Still, as many investors know, all bubbles do burst and while they’re eager not to get left behind when the IPO does come and their shares explode in value; they don’t want to be caught holding the bag should someone better come along pre-IPO and make Facebook look like a chump.

Until then, we will gain insight into Facebook’s trading from these new private market services, which appear to be yet another barometer of the anticipated success of privately traded companies.