Facebook Co-Founder Moskovitz Builds a Second Fortune With Asana (1)

When Dustin Moskovitz stepped away from Facebook Inc. four years after helping start the company, the 24-year-old owned a piece of the social-media giant that today would be worth about $18 billion.

Now he has another fortune to rival the first. Moskovitz has been vacuuming up shares of Asana Inc., the task-management company he left Facebook to create. Asana shares have skyrocketed more than 250% since mid-May, giving Moskovitz a stake valued at almost $8 billion, according to the Bloomberg Billionaires Index.

Moskovitz’s second act is a demonstration of Facebook’s power to mint new fortunes. Another co-founder, Eduardo Saverin, used ...