Facebook Inc. (FB) Chief Executive Mark Zuckerberg is sticking with his commitment to unload 35 million to 75 million shares during the next year and a half, disclosing he has sold $357 million worth in February alone.

First spotted by CNBC, the CEO of the leading social media network disclosed the stock sales were part of his plan to fund the Chan Zuckerberg Initiative, his philanthropic investment firm. In the Securities and Exchange Commission filing, Zuckerberg disclosed he made seven separate stock sales during the month. Back in September, he disclosed plans to sell 35 million to 75 million shares during the course of the next 18 months to fund his philanthropic plans. According to CNBC, when Facebook announced the planned stock sales, they would have been valued at $6 billion to $12.5 billion. Now, with the stock up, a sale of 75 million shares would generate $13 billion. Even with the share sales this month, Zuckerberg still owns 87% of the voting shares at the social media giant, reported CNBC. (See also: Facebook: Zuckerberg Sold $1B in Stock This Year.)

Second in a Series

This isn’t the first time in recent months that Zuckerberg has engaged in stock sales. In April of last year, Recode did an analysis of stock sales by Zuckerberg and found that he has unloaded more than $1 billion in stock in the 12 months leading up to that month. According to an analysis of Facebook’s annual proxy statement by Recode, Zuckerberg had around 9.6 million fewer shares at the end of March, when compared to the previous year. The shares at the time were valued at more than $1.3 billion. The report noted all of the proceeds will go to the charity run by him and his wife, Priscilla Chan. The couple has already committed $3 billion over the next 10 years to bankroll research aimed at curing all diseases. Based on the filing, the stock sales are expected to continue under his preset trading plan that requires him to sell or gift no more than $1 billion Facebook stock each year through 2018.

The stock sales, while regularly scheduled, do come at a time when Facebook could be losing a bit of its dominance to rivals. While Facebook is still the leader in terms of users and revenue, its growth is starting to stall as it faces increased competition from the likes of Twitter Inc. (TWTR) and Snap Inc. (SNAP). (See also: Facebook's Growth Threatened By Twitter, Snap.)

Daniel Ives, chief strategy officer and head of technology research for GBH Insights told CNBC recently that Facebook is no longer the only game in town for advertisers and that 20% of the social media’s advertisers are testing ads on Twitter and giving Snapchat a second look.

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