Is There a Cryptocurrency Bubble? Just Ask Doge.

Today, Mr. Palmer, 30, is one of the loudest voices warning that a similar fate might soon befall the entire cryptocurrency industry.

“What’s happening to crypto now is what happened to Dogecoin,” Mr. Palmer told me in a recent interview. “I’m worried that this time, it’s on a much grander scale.”

Already, there are signs of trouble on the horizon. This week, after Chinese authorities announced a crackdown on virtual currencies, the value of Bitcoin briefly tumbled 30 percent before partially recovering. The value of Dogecoin fell more than 50 percent last week. Its market value by midday Friday was about $100 million.

But there remains no bigger mania among tech investors than cryptocurrency, which some see as an eventual replacement for traditional, government-issued money. Even with the recent declines, the price of Bitcoin has more than tripled this year; another cryptocurrency, Ethereum, has gained more than 2,300 percent. The success of these currencies has minted a new class of “crypto-millionaires” and spawned hundreds of other digital currencies, called altcoins. In addition, it has given rise to an entire category of start-ups that take advantage of cryptocurrency’s public ledger system, known as the blockchain.

Many cryptocurrency start-ups have raised money through an initial coin offering, or I.C.O., a type of fund-raising campaign in which investors buy into a new venture using Bitcoin or another cryptocurrency and receive virtual “tokens” instead of stock or voting rights in the company. These tokens grant investors access to a product or service that will be built with the money raised in the I.C.O., such as cloud data storage or access to a new social network.

(If you’re having trouble picturing it: Imagine that a friend is building a casino and asks you to invest. In exchange, you get chips that can be used at the casino’s tables once it’s finished. Now imagine that the value of the chips isn’t fixed, and will instead fluctuate depending on the popularity of the casino, the number of other gamblers and the regulatory environment for casinos. Oh, and instead of a friend, imagine it’s a stranger on the internet who might be using a fake name, who might not actually know how to build a casino, and whom you probably can’t sue for fraud if he steals your money and uses it to buy a Porsche instead. That’s an I.C.O.)

Despite the obvious risks of these ventures, investor appetite has been ravenous. A group of Bay Area programmers this year used an I.C.O. to raise $35 million for their project, an anonymous web browser called Brave, in less than 30 seconds. There have been 140 coin offerings in 2017 that have raised a total of $2.1 billion from investors, according to Coinschedule, a website that tracks the activity.

I.C.O. fever has even infected celebrities. This month, the actress Paris Hilton tweeted that she was “looking forward to participating” in the initial coin offering of LydianCoin, a cryptocurrency project associated with the digital advertising company Gravity4. The boxing star Floyd Mayweather and the rapper the Game have also endorsed coin offerings.

Unlike traditional stock offerings, which are carefully supervised and planned months or years in advance, I.C.O.s are largely unregulated in the United States, although that could soon change. The Securities and Exchange Commission warned investors this year about the growing number of coin offerings, saying that “fraudsters often try to use the lure of new and emerging technologies to convince potential victims to invest their money in scams.”

Mr. Palmer predicts that while some I.C.O.s may finance the creation of new and exciting enterprises, many will go up in smoke. He sees echoes of the first dot-com boom, when investors poured money into new and risky ventures only to get burned when the market came to its senses.

“People are treating cryptocurrency now like penny stocks,” he said. “It’s become a securities market.”

Other high-profile skeptics have sounded the alarm about a potential crash in the crypto market, including Jamie Dimon, the chief executive of JPMorgan Chase, who last week called Bitcoin a “fraud,” and compared the current digital money craze to the 17th-century Dutch tulip bubble. And even true cryptocurrency believers have started to worry that I.C.O. mania won’t end well.

“It’s a ticking time bomb,” Charles Hoskinson, one of the developers of the cryptocurrency Ethereum, told Bloomberg in July.

When Mr. Palmer’s interest in digital money began, just four years ago, cryptocurrency was the sole province of math geeks and early adopters.

“It was fun, nobody took it seriously,” he recalled. “People threw it around like change because it wasn’t worth anything.”

Unlike Bitcoin, whose early adopters often used it to buy drugs, weapons, or other illicit goods on the dark web, Dogecoin attracted a crowd of earnest do-gooders at first. They even set up a philanthropic arm, called the Dogecoin Foundation, and used it to raise thousands of dollars for projects, including sponsoring service dogs for autistic children and drilling water wells in Kenya. (Their generosity extended to quirkier projects; when Dogecoin fans heard that Jamaica’s two-man bobsled team had qualified for the Winter Olympics in Sochi but lacked the money to get to Russia, they pitched in $30,000 to fund the trip.)

As the price of Bitcoin climbed, investors got interested in other cryptocurrencies. With no explanation, the price of Dogecoin doubled, then tripled. Two months after it was introduced, Mr. Palmer’s joke was worth $50 million, and some early Dogecoin adopters, who called themselves “shibes,” were sitting on lucrative stockpiles.

The success of Dogecoin attracted unsavory characters. One scammer raised $750,000 from Dogecoin supporters for a cryptocurrency start-up that never materialized. A hacker broke into Dogewallet, a website where users stored their coins, and stole thousands of dollars worth of the currency. Soon, the Dogecoin Reddit forum was full of angry scam victims and get-rich-quick schemers, and the once tight-knit Dogecoin community started to disintegrate.

“We tried to do everything right,” said Ben Doernberg, a former board member of the Dogecoin Foundation. “But when you have a situation where people stand to put in a dollar and take out a thousand dollars, people lose their minds.”

Mr. Palmer, a laid-back Australian who works as a product manager in the Bay Area and describes himself as “socialist leaning,” was disturbed by the commercialization of his joke currency. He had never collected Dogecoin for himself, and had resisted efforts to cash in on the currency’s success, even turning down a $500,000 investment offer from an Australian venture capital firm.

In 2015, he announced he was leaving Dogecoin behind, telling an interviewer that the cryptocurrency market “increasingly feels like a bunch of white libertarian bros sitting around hoping to get rich and coming up with half-baked, buzzword-filled business ideas.”

He recently began making a series of YouTube videos that explain tech topics to beginners, including how digital currencies work. His goal? To rekindle people’s excitement in the core blockchain technology, while tamping down some of the excessive hype.

“My mission in all of this is to help people better understand things, rather than just thinking about profit,” he said.

It may be too late for that. Regulators in the United States have begun to scrutinize I.C.O.s, and China’s central bank went as far as issuing a temporary ban on new coin offerings. But more dollars are still pouring into cryptocurrency ventures every day, as giddy investors ignore the warning signs and look to multiply their money.

Mr. Palmer worries that the coming reckoning in the cryptocurrency market — and it is coming, he says confidently — will deter people from using the technology for more legitimate projects.

“The bigger this bubble goes, the bigger negative connotation it’s going to have,” he said. “It’s going to be like the dot-com bust, but on a much more epic scale.”