Today’s tech titans came to power as disrupters of business models, eating away the profits of music stores, book publishers, video shops, newspapers and more. But another wave of disruption is just arriving — small enough to fit in your pocket and powerful enough to shake up much of Silicon Valley.

As sophisticated mobile devices begin to dominate the consumer marketplace, the peril is growing for the multibillion-dollar empires built on the popularity of personal computers.

The stakes may be obvious for Hew­lett Packard, Microsoft and Intel, which made the hardware, software and chips that powered so many personal computers. Perhaps more surprising is how Wall Street also is punishing two newer companies, Google and Facebook, whose products many consumers consider essential to their mobile experiences.

The problem for these companies is that they rely on online advertising for a huge share of their revenue. Although online advertising is tremendously lucrative when users of personal computers are the targets, that’s not yet true for mobile devices, which have smaller screens and don’t have the same track record of converting pitches to sales — especially when it comes to big-ticket items.

It’s the riddle many in the tech industry are desperate to solve.

“Here’s the scary thing: It’s not being disrupted by a lucrative new business. It’s being disrupted by a social reality,” Gartner tech analyst Whit Andrews said. “There’s not a big business yet in mobile advertising and mobile moneymaking. This is what scares people.”

One sign of the upheaval could be heard from Google chief executive Larry Page on Thursday, hours after a technical glitch caused the company’s disappointing earnings report to get posted ahead of schedule. He acknowledged the mixup with a quick apology but spent far more time on a subject he clearly regarded as more important: the company’s prospects for managing the mobile disruption.

Page focused on the promising number — Google’s revenue from mobile products was on its way to more than tripling for the year, to $8 billion — and played down the worrisome news that the money advertisers had paid per click was off by 15 percent compared with a year earlier. Driving this shift was the increasing share of ads appearing on the tiny screens of mobile devices instead of personal computers.

“We’re uniquely positioned to get through that transition and really profit from it,” Page said.

Investors saw it differently, driving Google’s stock down by 8 percent. It was down again Friday. So was Microsoft’s, which had its own disappointing earnings report Thursday. So was Intel’s. So was Hewlett Packard’s. Facebook was up modestly Friday but has fallen by half since its initial public offering in May.

Americans used 114 million smartphones in August, up from 101 million in the beginning of the year, according to comScore, which tracks the industry. The percentage of Web pages viewed from mobile devices reached 13 percent, up from 7 percent a year earlier. Worldwide shipments of personal computers, meanwhile, fell 8.6 percent in the third quarter compared with 2011, according to research firm International Data.

“That shows just how quickly this shift is happening, and it seems to be accelerating,” said Andrew Lipsman, vice president for industry analysis at comScore.

Consumers use tablet computers in ways that are not profoundly different from personal computers, surfing Web sites, seeing ads and making purchases. Smartphones mark a clearer departure. Web searches on such devices tend to be more contextual, relating to where users are at the moment.

More than one-third of smartphone users, for example, reported using their devices to engage in “showrooming,” meaning doing Internet research on a product they see in a store but making the eventual purchase elsewhere, comScore found.

The problem is so serious for retailers that BestBuy and Target have offered to match prices that shoppers find online. But advertisers potentially lose out, too, because that research does not always lead directly to a sale. Often shoppers will travel to a different brick-and-mortar store for a better price. Sometimes they return home, do more research on their desktop computers and only then complete purchases.

That less-direct connection between a search and a sale makes it harder for marketers to justify large advertising budgets, said Sam Bloom of Camelot Strategic Marketing and Media in Dallas. He said rates for ads on mobile search queries run about one-third less than for queries made from personal computers.

He, like Page, sees plenty of opportunity in mobile as marketers get more sophisticated in using location data to tune their pitches to where people are at the moment and what they are doing. “I think that’s the future. It’s just not the present,” Bloom said.

Many technology companies have plausible arguments for how they will manage the mobile disruption.

Microsoft will soon release its Surface tablet, a direct assault on Apple’s iPad, and its Windows 8 operating system, which was engineered to work elegantly on mobile devices. Facebook is pushing hard to better mon­etize its huge trove of personal data in more effective mobile ads. Intel can be reasonably confident that, in the long run, computers of all sizes will need fast chips.

Google, meanwhile, is even more dominant in mobile searches than it is in searches conducted from desktops or laptops. Plus, it owns the most popular smartphone operating system, Android.

But one company that looks even better positioned is Google’s arch-rival, Apple, analysts say. Its iPhone and iPad are massively popular in their respective mobile markets, with a new, smaller iPad expected to be announced next week. They have rich ecosystems of content to offer, which may increasingly be key to consumer buying decisions.

Wall Street, clearly, is pleased, having made Apple in August the most valuable company in the world.

But if there’s one immutable lesson of the technology industry and disruption theory generally, it’s that there’s always a next wave of disrupters massing somewhere beyond the horizon. In the case of mobile, that wave has arrived.