Activist hedge fund Elliott Investment Management said on Monday it had become Pinterest’s top shareholder and expressed confidence in the social media company’s potential to create value for investors. Pinterest shares were up 21% in pre-market trading Tuesday.

“Pinterest is a highly strategic business with significant potential for growth, and our conviction in the value-creation opportunity at Pinterest today has led us to become the company’s largest investor,” said Elliott Managing Partner Jesse Cohn and Portfolio Manager Marc Steinberg in a Monday afternoon statement.

The news confirms a Wall Street Journal report from two weeks ago that said Elliott had built a 9% stake in Pinterest and was holding talks with the company’s leadership. The activist did not disclose the size of its stake in the Monday release.

The company’s stock surged more than 20% above $24 each after the closing bell Monday, despite a disappointing earnings report. Pinterest said second-quarter revenue rose 9% to $666 million, its lowest growth figure in two years as users spent less time on the company’s platform. Pinterest also reported a net loss of $43 million, compared with a profit of $69 million a year ago.

Elliot, which manages more than $55 billion of assets, said it was supportive of CEO Bill Ready, who took over a little over a month ago, and Chairman Ben Silbermann “as they drive toward realizing Pinterest’s full potential.”

“We’ve had a very collaborative and engaged dialogue with Elliott recently. They’re aligned with our vision on what Pinterest can become, are supportive of our team and our efforts, and see the same tremendous potential for long-term value creation that I do,” Pinterest CEO Ready told analysts in a conference call Monday.