Elon Musk Takes 9.2% Stake in Twitter, Sending Shares Soaring

Elon Musk took a 9.2% stake in Twitter Inc. to become the platform’s biggest shareholder, a week after hinting he might shake up the social media industry.

Twitter shares surged as much as 27% after Musk’s purchase was revealed Monday in a regulatory filing. The gain marked the stock’s biggest intraday increase since its first day of trading following the company’s 2013 initial public offering. The stake is worth about $2.89 billion, based on Friday’s market close.

Musk, 50, polled his more than 80 million followers on Twitter last month, asking them whether the company adheres to the principles ...