Chris Hymel, Signal Advance's chief executive, was forced to put out a statement declaring that his company had "no association with … the entity, or platform, referred to by Mr Musk," adding: "Mr Musk is not, to the best of our knowledge, a shareholder."
Signal was an exceptional case, thinly traded and low-valued enough that even a small amount of trading was sufficient to spike the shares.
But Musk, 49, has emerged as a turbo-booster of multiple publicly traded stocks, adding fuel to recent amateur investing frenzies.
Last month, shares in the online marketplace Etsy briefly climbed 9pc when Musk tweeted that he used it to buy a wool helmet for his dog, styled after a Looney Tunes character.
CD Projekt, a Polish computer game maker, enjoyed a 19pc share price rise when he tweeted about Cyberpunk 2077, a recently released game.
And most notably, he gave a frenzied rush for shares in GameStop added momentum, tweeting: "Gamestonk!!" with a link to the Reddit trading forum at the centre of the movement. Within minutes, shares had jumped by 60pc.
Musk has a long history of market-moving tweets, but mostly about his own company. Last May, he tweeted Tesla's shares were "too high", sending them tumbling more than 10pc.
Most notoriously, he tweeted in 2018 that he planned to take Tesla private, adding: "Funding secured."
After it emerged that funding was not remotely secured, the US Securities and Exchange Commission forced Musk to step down as Tesla chairman, pay a $20m fine, and have tweets about Tesla's financial position checked by a lawyer.
But Musk is not chief executive of Etsy, CD Projekt or GameStop. "At Tesla it's different, because it's a company he controls," says Marketa Wolfe, a professor of economic sciences at Skidmore College in New York. "He cannot, as an individual, affect Etsy, unless he buys a million baskets."
Wolfe and Alexander Kurov, of West Virginia University, studied how another prominent Twitter user – Donald Trump – moved markets after his election. They found while the former president could induce short-term swings in companies such as Lockheed Martin, shares typically reverted to the norm soon after.
Kurov says even if only a tiny fraction of Musk's followers view a tweet as an endorsement, it could bring about a swing. "These traders could think if Musk is tweeting about this company, maybe there's some small chance that could be the next Tesla."
Studies have also shown that exposure itself can often drive investment in a stock, particularly among retail investors. In 2008, researchers at the University of Berkeley found individual investors are more likely to invest in "attention-grabbing" stocks – those that feature more prominently in the news.
With thousands of potential investments to choose from, those that spring to mind have a natural advantage.
Today, Musk's tweets generate more attention than many news stories, especially among traders who congregate on forums such as Reddit.
Johan Bollen, a professor at Indiana University whose research has suggested that wider Twitter sentiment can predict the stock market, says many traders may buy shares Musk tweets about merely in anticipation that others will.
"People start to have these theories of mind where they start to think, 'A lot of people follow Elon Musk, and he just said that the company is good.' They start to speculate about what other traders will do."
Adding to this complexity, Bollen says, may be trading algorithms linked to social media sentiment. Musk's followers often retweet his comments tens of thousands of times, which may have an outsized impact on such algorithms.
Joe Gits, whose company Social Markets Analytics sells data about Twitter sentiment to hedge funds, says Wall Street traders are certainly paying attention to Musk's tweets.
The increasingly clear power of Musk's Twitter account may make it a target for regulatory attention or hackers. Last July his profile was caught up in a widespread hack as part of a cryptocurrency scam, alongside those of Joe Biden and Bill Gates.
Speaking on the audio app Clubhouse last week, Musk himself acknowledged his influence. "I gotta watch what I say here because some of these things can really move the market," he said, when asked about Bitcoin. Not long after, he said he was taking a social media break.
But just two days later, Musk was back, breaking his silence by tweeting: "Dogecoin is the people's crypto," in reference to a rival cryptocurrency created as a joke. Its value promptly surged, climbing by more than 50pc.
Musk's reluctance to intervene apparently only goes so far.
