Facebook insiders will be unloading more of their shares in the initial public offering, the company has said, as they take advantage of investor demand.
Facebook said in a regulatory filing on Wednesday that about 421 million shares will be sold, up from 337 million under its earlier plans.
The entire increase comes from insiders and early investors, so the company will not benefit from the additional sales.
The news comes a day after Facebook raised the expected price range for the stock to a range of $34 to $38 per share, up from its previous range of $28 to $35.
If all the shares being offered - including more than 63 million more shares that the deal's underwriters can sell to cover excess demand - are sold at the high end of the expected price range, the social network's offering could raise more than $18.4bn.
That would make Facebook one of the biggest IPOs ever.
The IPO is the most hotly anticipated in years and would value Facebook overall at more than $100bn.
In a filing with the Securities and Exchange Commission, Facebook said current shareholders are now offering approximately 241 million shares, up from about 157 million shares previously.
The additional stock sales will reduce CEO Mark Zuckerberg's voting control to 55.8 per cent from 57.3 per cent.
He is not selling more of his own shares than previously announced, but has voting control over some of the additional shares to be sold.
Facebook has more than 900 million users who log in at least once a month, but it makes only a few dollars per year from each one, chiefly through advertising.
Advertisers have been complaining that it is difficult to make good use of Facebook.
Against this backdrop, major advertiser General Motors Co said on Tuesday it would stop advertising on Facebook.
GM did not say why it would stop advertising.
The Wall Street Journal reported, citing people it did not identify, that it was because GM had concluded that the ads were ineffective.
Greg Martin, GM spokesman, said the company will keep paid content on pages that promote its products. Meanwhile, GM competitor Ford reaffirmed its commitment to Facebook, saying its relationship was stronger than ever.
Morgan Stanley leads the team of 33 underwriters selected for the Facebook offering, followed by JPMorgan Chase and Goldman Sachs.
The offering is expected to set the final price on Thursday evening. Shares would start trading on the Nasdaq on Friday under the "FB" ticker symbol.