Facebook has been valued at $65.5 billion (€45bn) in a significant share sale ahead of its expected initial public offering next year. Interpublic, the advertising group, sold half of its 0.4 per cent stake in Facebook for $133 million (€92m) to an undisclosed buyer.

The sale is likely to put the spotlight back on to the secondary market for private company stock.

Facebook’s implied valuation has increased more than fivefold in less than two years, driven largely by demand for small stakes in the company available on the secondary market. Interpublic, which owns McCann Erickson and other advertising agencies, disclosed its Facebook stake in a filing with the US Securities and Exchange Commission earlier this year after it grew to a value of more than $200 million.