Trading app Robinhood on Thursday restricted buying or trading in GameStop stock along with several other formerly obscure stocks that are spiking following a scramble of social media driven trading activity this week. The popular stock market app informed users that they could close out positions on the highly volatile stocks but could not purchase additional shares. “We continuously monitor the markets and make changes where necessary. In light of recent volatility, we are restricting transactions for certain securities to position closing only,” including GameStop, AMC Entertainment, BlackBerry, Bed Bath & Beyond, Express, Koss, Naked Brand, and Nokia, Robinhood said in a statement. Online broker Interactive Brokers also restricted trading for GameStop, AMC, BlackBerry, Express, and Koss to “liquidation only,” the company said in a statement Thursday. Both companies said they have also raised margin requirements for certain securities. GameStock shares quickly sank in response to the news of the restrictions. The company’s shares had skyrocketed this week to above $400 from less than $19 at the end of 2020. Robinhood, which has about 13 million users, was a key tool in efforts by a group of Reddit users from the subreddit WallStreetBets who plotted to push the stock of GameStock and several other companies higher in an attempt to undermine traditional Wall Street hedge funds that had shorted the companies. Several hedge funds have already seen major losses in the wake of the chaos, including Citron Research and Melvin Capital, which was force to obtain a nearly $3 billion cash injection to cover its losses. A day earlier, Charles Schwab and TD Ameritrade also restricted trading on GameStop and AMC. “We’re committed to helping our customers navigate this uncertainty,” Robinhood said in a blog post.