Saudi Arabia: Saudi Arabia’s Prince Alwaleed bin Talal announced the purchase of a $300 million investment in Twitter, expanding his media empire into social-media sites and giving the billionaire a stake in an online forum that was widely used by activists in this year’s Arab uprisings.

Saudi Prince Alwaleed bin Talal. Photo: Bloomberg

Unlisted Twitter was valued by analysts in October at about $8.4 billion, suggesting that Prince Alwaleed’s stake is equivalent to 3.6% of the company.

Twitter, which allows users to send messages called “tweets" of up to 140 characters each, said recently it had grown to 100 million active users who cumulatively send 250 million tweets per day. Facebook Inc., by comparison, has more than 750 million users.

“Social media will fundamentally change the media industry landscape in the coming years. Twitter will capture and monetize this positive trend," Ahmed Halawani, executive director of private equity and international investments at Kingdom Holding, said in the same statement.

Prince Alwaleed, a nephew of Saudi King Abdullah, had been cited in news reports since October as pursuing a purchase of Twitter shares from one of the co-founders of the social media company. Kingdom Holding officials didn’t provide any further details of the purchase early Monday. Matt Graves, a Twitter spokesman, confirmed the investment but declined further comment.

“I see him as an investor happy to invest in any industry that he might think is lucrative at any stage," Reda Haidar, a media and Internet analyst based in the United Arab Emirates, said by telephone.

Amir Efrati in San Francisco contributed to this article.