Restrictions preventing employees from selling 229m shares came to an end, sparking the staff sell-off and rattling Facebook’s broader pool of investors. It prompted the biggest fall in the social network’s value for five weeks.

The so-called lock-up period was imposed to stop a flood of shares hitting the market immediately after the company’s May flotation, meaning many of the workers it turned into paper millionaires could only stand by as their investments nearly halved in value. Facebook’s share price has dropped as much as 50pc since its disastrous $104bn flotation. Its market capitalisation stood at $45.5bn on Thursday, after shares in the social network fell 0.94 to $21 by mid-afternoon trading in New York.