Facebook’s initial public offering just keeps growing. The social network announced this morning via an amended S-1 filing that it will add around 84 million shares to its IPO, an increase of around 25 percent.

Come Friday, when the company is scheduled to begin trading on the Nasdaq under the symbol “FB,” Facebook will be floating around 421 million shares. The company’s stock is expected to receive its official pricing on Thursday, and Facebook says it will be in the $35 to $38 per share range.

If Facebook’s stock gets priced at the $38 high-end, its IPO would raise more than $16 billion and would make it the largest technology public offering ever, Fortune points out. AT&T Wireless, the current technology IPO leader, raised more than $10 billion in 2010.

The additional shares are coming from current Facebook investors Peter Thiel, Tiger Global Management, and James Breyer from Accel Partners, and not from Facebook itself. For that reason, the added shares won’t increase Facebook’s valuation.

Facebook CEO Mark Zuckerberg’s voting power will be reduced from around 57.3 percent to about 55.8 percent due to the new shares. That’s not ideal news for Zuck, but as long as he maintains his majority voting power, he’ll still be able to rule the company as he sees fit. The additional shares likely were a bid to appease the company’s existing investors.

Facebook yesterday added an additional $50 million shares to its IPO, with the caveat that they were part of an “over-allotment” option. We also heard yesterday that General Motors is planning to stop running ads on Facebook, after determining that they were ineffective.

Photo via Jim Merithew/Wired