GameStop Corp on Monday increased the value of new stock it may sell from $100 million to $1 billion, as the U.S. video game retailer seeks to capitalize on a surge in its shares from a Reddit-driven rally this year. GameStop stock has rampaged over 900% higher since January in highly volatile trading as amateur investors organized on social media sites such as Reddit staged a stubborn buying spree, winning out over Wall Street hedge funds that had shorted its shares. GameStop's shares fell as much as 13.9% on Monday. They briefly reversed course to trade up slightly, but were trading lower again at 11:53 a.m. EDT at $188.50.