Social-networking site Facebook is halting the sale of its shares on secondary markets effective next week, aiming to reduce churn in its valuation which could complicate matters as it sets an IPO price, a person familiar with the situation said on Wednesday.

The company, which is preparing for what could be Silicon Valley's largest initial public offering, has asked firms that arrange trading of its privately held shares to stop, the person said.

Earlier this week, one of the firms that arranges trading in Facebook shares, SharesPost Financial, told investors it was moving up the closing date for its Facebook auction to March 30 from April 2.

Facebook filed its paperwork to go public in early February. Its IPO, expected to value the company at around $100 billion, is expected in coming months.

A Facebook spokesman declined to comment. Representatives at SharesPost and SecondMarket, another firm that arranges trading in private shares, didn't immediately respond to requests for comment.

Bloomberg reported the news earlier Wednesday.