Facebook (FB) CEO Mark Zuckerberg to sell 70 million shares

Facebook (FB) stock fell Thursday after the company said in a regulatory filing that CEO Mark Zuckerberg plans to sell more than 40 million shares as part of the company's first follow-on stock offering, which will total about $4 billion.

Facebook stock was down 2.4% in midday trading in the stock market today. The stock fell as much as 5.2% in heavy pre-market trading Thursday, according to the Nasdaq exchange.

Zuckerberg plans to buy 60 million Class B shares as part of a longstanding option, and 41.4 million of those shares will immediately convert to Class A shares and be sold, according to the filing.

At Thursday's midday price of 54.16, Zuckerberg would get about $2.24 billion, which the company he'll mostly use to pay taxes on the 60 million share option.

The action is part of a secondary stock offering in which the company will sell 27 million shares. Shareholders, including Zuckerberg, will sell about 43 million shares.

The follow-on offering is the company's first since its May 2012 initial public offering, which raised about $16 billion.

The new sale will knock Zuckerberg's holdings to 56.1% of the company's voting power, down from 58.8%, according to Facebook.

The approximately $1.46 billion that the company will raise in the offering will be used for general working capital, says Facebook.