When Facebook shares hit the market at US$38 and moved to a high of US 45 dollars after the massive IPO in the US, life looked good with the company, valued then at US 100 billion but the shares are currently 50% of these highs.

Yesterday saw the expiration of a "lock up" period and the shares fell a further 6% as markets anticipate the possiblity of huge share parcels coming onto the open market. 

A lock-up is an arrangement put in place before the company's shares go public for the first time, to avoid the initial share price collapsing as the investors who own part of the company try and cash in on the profits they have.

This is a standard share price supporting strategy but in this case, the shares were already considered overpriced and there are still billions of Facebook shares locked up for longer periods, well known to market investors and this can tempt bear sellers of the stock to push it further down, as the company struggles to monetise the enormous global membership, estimated at 900 million.

There are further Investor lock up expiration dates that will impact on the shares negatively over the next two years