GameStop’s shares soared on Monday after the long-dormant Reddit account associated with Keith Gill, the trader known as Roaring Kitty who helped spur 2021’s meme-stock mania, appeared to show a big stake in the video game retailer.

It was GameStop’s second major rally in as many months, seemingly prompted by social media buzz. The stock more than doubled at one point in premarket trading, before settling to a gain of about 70 percent, a move adding billions of dollars to the company’s market value.

Monday’s surge was driven by a screenshot uploaded to Reddit on Sunday by the account associated with Mr. Gill, after more than three years of inactivity. The post showed a holding of five million shares in GameStop worth just under $116 million, nearly $30 million in cash and a large number of options that give the holder the right to buy more stock at $20 per share. The market data provider Unusual Whales posted that there had been a spike in trading for those options.

Adding fuel to the rally was a post to the X account associated with Mr. Gill that featured an image of a reverse card from Uno, the card game. Followers largely interpreted the picture — in line with the cryptic memes that punctuated Mr. Gill’s social media posts in 2021 — as a rallying cry to bolster GameStop’s stock price, which had fallen after a Roaring Kitty-inspired spike last month.

GameStop benefited from that rally by selling new shares, raising $933 million. The move “prudently” gives GameStop “a greater level of reserves while it struggles to refocus its business and reverse continuing operating losses,” according to a recent research note by analysts at Wedbush.

The new posts continue a flurry of activity from Mr. Gill’s accounts, which had been quiet since 2021. The X account TheRoaringKitty resumed posting on May 13, with another cryptic meme largely interpreted as a pro-GameStop call, followed by dozens of rousing clips from television shows, movies and music videos.

Online sleuths have been debating the revival of the accounts since last month, with some speculating that Mr. Gill had sold his X account to a conceptual artist with a history of trolling. While Mr. Gill’s X and Reddit accounts have shown signs of life, his YouTube channel — where he regularly posted videos of himself talking up his stock recommendations — remains inactive.

Mr. Gill gained a cult following during the coronavirus pandemic with lively videos and posts arguing that GameStop was undervalued. In 2021, that stock and others, like AMC Entertainment, soared in value as armies of small investors piled in and cheered each other on with irreverent memes. The chaos inspired the 2023 film “Dumb Money.”