Tesla CEO Elon Musk has taken a 9.2 percent stake in Twitter, according to a regulatory filing, becoming the social media giant’s biggest individual shareholder just weeks after questioning the platform’s attitude towards free speech. Musk bought 73.5 million shares of Twitter on March 14, according to a Securities and Exchange Commission (SEC) filing released Monday. Based on Twitter’s closing price on Friday, Musk’s stake was worth $2.89 billion. News of the purchase sent Twitter shares soaring by over 20 percent in pre-market trading Monday, sharply boosting the value of Musk’s stake. Musk tweets regularly on the platform, where he has over 80 million followers. In a March 25 tweet, Musk wrote that “free speech is essential to a functioning democracy” and asked his followers whether they believe Twitter “rigorously adheres” to this principle. In a follow-on tweet, Musk asked his followers to “vote carefully” as the “consequences of this poll …