Elevation Partners, a fund that includes U2 singer Bono as one of its investors, has dropped its shares in Facebook, once valued at $1.3bn and now valued at $650m, as the social media company's stock continues to plummet, reports the Herald.

When Facebook went public three months ago, its founder, 28-year-old Mark Zuckerberg became the 23rd richest man on earth with a fortune valued as €15bn.  That has number has now almost halved, knocking Zuckerberg off the list of the world's top 10 wealthiest technology entrepreneurs as determined by this month's Bloomberg Billionaires index.

Investors worry that the shares, which hit a record low last week, may drop even  further, and investors, who had been blocked from selling shares until now, are debating whether to sell at the current price or take a wait and see approach and hope for the prices to turn around.

According to the Herald, PayPal co-founder Peter Thiel, a backer of Facebook in its infancy, has recently converted all his shares, whose value has dropped from over e800m to e453m, to a form that can easily be sold.

The investors holding the 271 million shares in Facebook were free to sell them for the first time on Thursday due to a 90-day rule to prevent insider trading.

Bono received the Freedom of Dublin in 2000