SAN FRANCISCO — Another couple of days like this and the great tech bubble of 2012 might recede into history.

Several companies that were supposed to be the foundation of a new Internet era plummeted last week as analysts and investors downgraded their dreams. There were parallels to the crash of 2000, when the money stopped flowing, the dot-coms crumbled and Silicon Valley devolved into recriminations and lawsuits.

Shares of Facebook stumbled to a new low Friday after its first earnings report revealed a murky path to any profit that would justify its lofty valuation. The heavily promoted $100 billion company on the eve of its May debut is now a $65 billion company — and headed south.

Zynga, the social games company that uses Facebook as a platform, was battered even worse Thursday, leaving its value at less than a quarter of its peak last winter. Netflix, which is trying to move from DVDs to streaming video, and the coupon company Groupon have also been under severe pressure, leaving them at a modest fraction of their recent worth.

Feelings of disillusionment are far from universal. Social media is flourishing; a billion Facebook and 500 million Twitter users would vouch for that. But as just about every Internet company is grappling with the transition to a mobile world, turning groups of people into cash-generating customers on a hand-held device is clearly an immense task.

Nick Zaharias, an independent consultant who advises institutional investors, said his clients were “infinitely” more skeptical. “For future deals that are pitched as social deals, they’re not going to pay up.”

Why the slump?

The issues facing each tumbling company are slightly different. But they all have the problem of selling something — imaginary tractors, Internet films, discount deals or, in Facebook’s case, someone “liking” a product — that is not quite real and perhaps less than essential.

“The gleam has come off the word ‘social,’ ” said Ben Schachter, an Internet analyst with the Macquarie Group. “The ground is now shifting underneath these companies’ feet at a speed that we didn’t see even in the late 1990s.”

Groupon and Netflix have been in the investor doghouse for a while; with Facebook there seems simple regret that its grandest ambitions might not be reached. “The jury is in: Facebook is not and will not be a second Google,” the research group IDC said.

With Zynga, however, there was a sudden sense that building a blue-chip business from virtual goods might be virtually impossible.

“Shocking,” Schachter wrote in his report after Zynga revealed in its earnings report Wednesday that it might make less than half of what it had hoped to earn this year from its more obsessive players who pay actual money for virtual goods like tractors — its only real source of income. Increasingly, gamers want to play on the run, and Zynga’s mobile games are not a runaway success.

For all the pain that stockholders of Zynga and the other companies must feel, it is not yet March 2000, when all tech stocks went into free fall. The old-line companies, including Google, Amazon and Apple, are doing fine.

But the questions about whether the CEOs and other early investors in some once-hot companies might have been a little too eager to cash in are already beginning, just as they did 12 years ago.

Two sides to investing

Early investors in Facebook increased their participation in the public offering at the last minute by more than 80 million shares, netting them nearly a billion dollars more than the shares would have fetched Friday on the open market. (Mark Zuckerberg, Facebook’s founder, was not among those increasing their allotment.) Zynga’s founder, Mark Pincus, sold 16 million shares in an unusual secondary offering four months after the December public offering. He and other executives got $12 a share in those more optimistic times, four times the Friday price.

Pincus was asked about those sales Wednesday during the analyst conference call by the BTIG analyst Richard Greenfield. “I wanted to see whether he felt bad about it,” Greenfield said later. Pincus did not address the point.

If investors were battered and Wall Street was alarmed, Silicon Valley was unfazed.

The downward slide in public valuations would have an effect on private valuations, venture capitalists said, but it would be manageable.

Some of the biggest venture capital firms have raised giant funds in recent months. New Enterprise Associates has announced, for instance, that it raised $2.6 billion for its latest fund — the second-largest in venture history. Valuations, particularly those at the later stage, have tightened a bit, but plenty of younger startups are still raising seed capital at lofty valuations.

“Venture capitalists tend to think long term,” said Peter Barris, NEA managing general partner. “The daily ups and downs in the stock market you’ve got to take with a grain of salt when you’re looking at new investments and what they might be worth (later).”

One blessing and one problem with investing in tech companies is that the pace of their development has increased. A startup’s initial sprint can be exciting, but it can also make it difficult to pinpoint when growth will start to decelerate. “Companies can grow into their markets faster than ever before but that means they can reach saturation faster than ever before,” said Roelof Botha, a partner at Sequoia Capital.

In what has become a common refrain, many venture capitalists say Silicon Valley is rich with investment opportunities, because the world of 2012 is vastly different from the dot-com era. As the argument goes, it has never been easier to create a global startup out of the box. The number of people connected to the Web is unprecedented. And so on.

In other words, the bubble will not pop, because this time it is different.

Apple considers stake in Twitter

Apple, which has stumbled in its efforts to get into social media, has talked with Twitter in recent months about making a strategic investment in it, according to people briefed on the matter.

While Apple has been successful in selling phones and tablets, it has little traction in social networking, which has become a major engine of activity on the Web and on mobile devices. Social media are increasingly influencing how people spend their time and money — an important consideration for Apple, which also sells applications, games, music and movies.

Apple has considered an investment in the hundreds of millions of dollars, one that could value Twitter at more than $10 billion, up from an $8.4 billion valuation last year, these people said. They declined to be named because the discussions were private.

There is no guarantee that the two companies, which are not in negotiations at the moment, will come to an agreement.

Apple has not made many friends in social media. Its relationship with Facebook, for example, has been strained since a deal to build Facebook features into Ping, Apple’s music-centric social network, fell apart. Facebook is also aligned with Microsoft, which owns a small stake in it. And Google, an Apple rival in the phone market, has been pushing its own social network, Google Plus.

“Apple doesn’t have to own a social network,” Timothy Cook, Apple’s chief executive, said at a recent conference. “But does Apple need to be social? Yes.”

— New York Times News Service