Bitcoin's value jumped more than 20% to $38,566 on Friday after Elon Musk, the world's richest person, changed his personal Twitter bio to #bitcoin, fueling speculation that he had bought more of the cryptocurrency.
Less than 24 hours earlier, the billionaire appeared to prompt shares in CD Projekt, which makes the Cyberpunk 2077 computer game, to surge more than 12% after he said via Twitter that a new model of Tesla's Model S Plaid car would allow passengers to play the game.
Several hours later, Musk said, "With Cyberpunk, even the hotfixes literally have hotfixes, but … great game."
On Tuesday, the Tesla and SpaceX CEO fueled the frenzied surge in GameStop shares when he tweeted "Gamestonk!!" and a link to the WallStreetBets Reddit thread. The made-up word is a combination of GameStop and "stonks," which is a slang term for stocks.
"There's an odd irony to Elon Musk's ability to move the market, while attacking what he sees as unnatural market forces in short-selling," Dan Lane, an analyst at British trading app Freetrade told CNBC. "It might be that this is finally the time to have a discussion on the legitimacy of the practice."
The tweet appeared to help GameStop's valuation to skyrocket to more than $10 billion in after-hours trading and resulted in some amateur trading apps to pause trading. But some people stand to lose a lot of money if GameStop's share price comes crashing down.
Vincent Flood, presenter of the "VideoWeek" podcast, which looks at the advertising market, said Musk's tweets can "have devastating consequences for retail investors whilst he and his friends enrich themselves at the expense of the little guy."
Ex-Googler Rich Pleeth, an entrepreneur and tech investor in London, agreed. He told CNBC that Musk can "enrich himself with one tweet."
"He is an innovator but that doesn't mean he's above the law," Pleeth said.
However, Max Levy, head of business development at online investment management app Nutmeg, said, "This has always happened in capital markets," listing Warren Buffett and Ray Dalio as other "influencers" on asset prices.
The Securities and Exchange Commission, a regulator set up in the 1930s to protect investors, declined to comment when CNBC asked if it was concerned at Musk's ability to influence stocks on Twitter.
The New York Stock Exchange also declined to comment, while the tech-focused Nasdaq stock exchange, and a representative for Musk did not immediately respond to CNBC's request for comment.
Musk has faced problems with the SEC for tweeting about Tesla's stock. In August 2018, he said he wanted to take Tesla private at $420 per share and that he had secured the funding to do so. Musk and Tesla each had to pay the SEC a $20 million fine to settle the suit, and Musk has since agreed to submit his public statements about Tesla's finances and other topics to vetting by its legal counsel. He infamously tweeted last year that Tesla's stock was "too high," sending shares down more than 10% immediately, though they more than rebounded within a week.
While Musk's Twitter actions have had a particularly pronounced affect this week, he's been shifting stocks and cryptocurrencies for a while now. Earlier this month, Musk urged his 48.3 million followers to use encrypted messaging app Signal, which is operated by a nonprofit.
Keen to back the company, investors rushed to snap up shares in Signal but many of them accidentally bought shares in a small components producer called Signal Advance, sending its stock up 1,100%.
"Regulators don't just need to catch up, they need to proactively enforce rules and clarify what is acceptable," Freetrade's Lane said. "And that goes for the shorts, too."
Lane added: "The reality is that the new brand of charismatic leader has a public platform now and isn't confined to the boardroom. It's up to regulators how they deal with that but, eventually, the onus will be on them to update the rule book."
Hussein Kanji, a venture capital investor in London, told CNBC that he trusts the SEC to do its job and keep markets rational and fair.
"But Elon Musk acting as an ultimate influencer and driving demand in a regulated securities market seems odd," said Kanji. "If he was moving volume for a consumer product, I wouldn't raise an eyebrow."
Steven Bartlett, founder of social media agency The Social Chain and a tech investor, told CNBC that "the public markets now have influencers like fitness and beauty do."
Musk has become the Zoella of public markets and there's no way around it for the SEC, Bartlett said.
— Additional reporting by CNBC's Jessica Bursztynsky.