Facebook is one of the biggest things in Silicon Valley at the moment and the social media giant is showing no signs of slowing down. It is being valued at several billion dollars, over 10, by previous transactions but since it's a private company, no one can really tell what it’s worth. However, despite the fact that Facebook isn't listed on any stock exchange, some shares end up on places like SecondMarket and SharesPost, which allow people who own Facebook common stock, mostly employees or former employees, to trade it. And prices for those shares have been going up over the past months to the point where Facebook's common stock is now worth around $9.5 billion.

That figure may be a bit misleading but it gives a rough estimate of what most people think the social network is worth. The $9.5 billion number is based on the price of shares currently being traded on SecondMarket, which has reached $21. The price has shot up 42 percent in the past four months, according to Bloomberg. This is just for the common stock though, as a chunk of the company is tied up in preferred stock, which is usually owned by venture capital investors so by this metric, Facebook may be worth more than $10 billion at the moment.

The valuation does seem very high but it's not the highest the social network has got; in fact, a couple of years ago, Microsoft bought a small share in the company at the ridiculous valuation at the time of $15 billion. The Redmond-based software giant wants to make an investment but rather place a stake and assure that Google doesn't come sniffing around Facebook any time soon.

Since then, Facebook's valuation has been all over the place as analysts tried to one-up each other in coming up with new numbers. The latest actual figures come from last summer when Russian firm DST bought a stake in the company at a $10 billion valuation. It also bought common shares at the lower $6.5 billion valuation.