Mark Zuckerberg's stake in Facebook has climbed to nearly 30 percent since the leading social network made its dismal stock market debut, according to a filing Wednesday with US regulators.

Zuckerberg owns 632.65 million Facebook shares as compared with the slightly more than 500 million he held in September when the stock's sagging price prompted a promise he would not sell any for at least a year.

Zuckerberg sold about 30 million shares when the Menlo Park, California-based social network made its stock market debut in May at an opening price of $38.

Shares slid to a low of $17.55 in September but have regained ground, trading at $28.04 at the close of trading on the Nasdaq exchange on Wednesday.

Securities and Exchange Commission filings show Zuckerberg has been building his stake Facebook, the potential of which he contends is underestimated by the market.

One SEC filing showed that Zuckerberg acquired 18 million Facebook shares in mid-December at a price of zero, indicating they were tied to his compensation as chief of the social network.