Robinhood Markets Inc. unveiled striking growth figures on Thursday in the paperwork for its long-awaited initial public offering-and long list of growing pains.The stock-trading app counted 18 million users with funded accounts at the end of March, more than double a year earlier. Revenue in the initial quarter of 2021 more than quadrupled to $522 million. The daily average number of cryptocurrency trades of Robinhood expanded by a factor of 14, and the net value of cryptocurrencies held in Robinhood users’ accounts increased to $11.6 billion from $481 million.Meanwhile, users transferred their assets out of Robinhood at almost 10 times the average rate after it curbed trading in Gamestop Corp. and other high-flying stocks in January, a decision that also resulted in roughly 50 class-action lawsuits. Around 81% of its initial quarter revenue came from a practice criticized by the chair of the Securities and Exchange Commission. And the company is facing a raft of investigations, with federal prosecutors going so far as to engage a search warrant to grasp the cellphone of Chief Executive Vlad Tenev.Robinhood, which plans to list on the Nasdaq under the ticker HOOD, is set to be the buzziest company to tap the US IPO market this summer especially since up to 35% of its offering is being allocated to its own trading clients. The listing could value the stock Executive Vlad Tenev.