Despite a return of volatility on Wall Street over the past couple of weeks, it looks like it will be another special year for equities. Through Wednesday, Dec. 15, the widely followed S&P 500 had logged 67 record-closing highs in 2021. Its year-to-date return of 25% has also more than doubled its average annual total return of 11%, including dividends, since 1980.

However, a rapidly rising and arguably pricey market hasn't stopped billionaire money managers from putting their money to work in the growth stocks that've been largely responsible for leading these rallies since March 2020. Based on 13F filings with the Securities and Exchange Commission, billionaires can't stop buying these four fast-growing stocks.

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Pinterest: Ole Andreas Halvorsen (Viking Global Investors)

First up is billionaire Ole Andreas Halvorsen, who manages more than $36 billion for Viking Global investors. During the third quarter, Halvorsen and his team couldn't get enough of social media up-and-comer Pinterest (PINS -0.70%). Viking Global opened a 7.23 million-share position in the company that was worth approximately $368 million at the end of September.

Although most pandemic plays have struggled in 2021 as vaccination rates ticked up and social life returned to some semblance of normalcy throughout the country, Pinterest's shares have been hit especially hard. Over the past two quarters, Pinterest has delivered sequential declines in monthly active users (MAUs), and Wall Street has been unrelenting in its punishment of the stock.

But Halvorsen appears to recognize a value when he sees one. Even with two consecutive sequential quarterly declines in MAUs, Pinterest isn't having any issue monetizing its user base. Despite year-over-year MAU growth of less than 1% in Q3, average revenue per user globally and internationally jumped by 37% and 81%, respectively. This clearly shows that Pinterest has strong ad-pricing power, and merchants are more than willing to pay a premium to get their message in front of the company's 444 million MAUs.

Furthermore, as I've previously noted, Pinterest's platform is the perfect middleman between online shoppers and merchants looking for customers. The entire premise of Pinterest is for users to share with the world the things, places, and services that interest them. All Pinterest has to do is connect users with merchants who can meet their interests. In other words, the platform allows for highly targeted advertising.

With a price-to-earnings-growth (PEG) ratio near 1, Pinterest looks like a bargain.

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Zoom Video Communications: Jeff Yass (Susquehanna International)

Another billionaire who's been unable to keep his distance from growth stocks is Jeff Yass from Susquehanna International. Yass, who's overseeing $745 billion in assets under management, has had an insatiable appetite for shares of Zoom Video Communications (ZM -0.49%). During the third quarter, Susquehanna increased its existing stake in Zoom by 2.47 million shares, or 274%, from the sequential quarter.

Not to sound like a broken record, but cloud-based web-conferencing company Zoom has also been a victim of its own success throughout most of 2021. With some workers returning to the office, Zoom's triple-digit sales growth has normalized to double-digit levels. That became a problem for a company that was, at one time, valued at a multiple of well over 50 times sales.

However, Yass sees utility in Zoom that extends well beyond pandemic euphoria. The past 21 months have shown how valuable its services can be in facilitating hybrid work environments and keeping projects on track, even when back at the office. Zoom's leading share of web-based conferencing in the U.S. is unlikely to be rivaled anytime soon.

Zoom is also looking well beyond web-conferencing for revenue channels. For instance, Zoom Phone, the company's cloud-based phone system, provides users with a digital alternative to legacy communication platforms.

A final thing for investors to consider is that CEO and founder Eric Yuan remains a large shareholder. Founders who remain active and retain a lot of skin in the game tend to put the interests of shareholders at the forefront.

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Palantir Technologies: Jim Simons (Renaissance Technologies)

Tech-stock darling Palantir Technologies (PLTR -0.44%) is another fast-growing stock being scooped up by billionaire money managers. In particular, Jim Simons of Renaissance Technologies couldn't get enough Palantir in the third quarter. Renaissance, which oversees more than $77 billion in assets under management, acquired north of 12.1 million shares of Palantir in the September-ended quarter.

Keeping with the theme, Palantir has not had the best year. But unlike Pinterest and Zoom, it has little to do with the pandemic. Rather, Palantir has been criticized for its valuation, which has, at times, topped a multiple of 40 times sales.

While such a hefty valuation multiple might be difficult to digest, Simons seems to understand that no other public company can provide what Palantir can. The company's data-mining-driven Gotham platform is used by the U.S. federal government to cull and organize large amounts of data, as well as to handle missions. Meanwhile, Palantir's Foundry platform is targeted at enterprise customers and aims to streamline their operations by making big data easier to understand.

For the time being, large U.S. military contracts that span multiple years have propelled the company's sales growth to 40% on an annual basis, or higher. But it's Foundry that offers more long-term promise. Since Gotham's usage is somewhat limited outside the U.S., Foundry has a considerably larger pool of potential customers that would benefit from better understanding complex data.

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Meta Platforms: John Overdeck and David Siegel (Two Sigma Investments)

Last but not least, billionaires John Overdeck and David Siegel, who run Two Sigma Investments, haven't been able to stop pushing the like button on Meta Platforms (META -0.07%), the company formerly known as Facebook. During the third quarter, Two Sigma gobbled up almost 535,000 shares of Meta, valued at $181.5 million, as of Sept. 30.

Overdeck's and Siegel's love for Meta likely springs from the overwhelming success of social-media platform Facebook. In Q3, 2.91 billion MAUs visited Facebook, with an additional 670 million MAUs heading to one of Meta's other owned assets (WhatsApp and Instagram). That's 3.58 billion people -- more than half of the global adult population -- visiting a Meta-owned asset at least once a month. It's no surprise that the company has exceptional ad-pricing power.

The crazy thing about Meta Platforms is that it hasn't even meaningfully monetized WhatsApp or Facebook Messenger. It'll generate more than $100 billion in ad revenue this year, nearly all of which will originate from Facebook and Instagram. If and when the company does monetize these channels, another surge in sales and profit potential should be expected.

Overdeck and Siegel are also probably excited about Meta's focus on the metaverse -- a next-generation iteration of the internet that allows users to interact in 3D virtual environments. The plan is for the company to spend $10 billion on metaverse investments in 2021, with successively higher spending in subsequent years.

If Meta can become a key player in virtual and augmented reality, it'll offer a second massive growth opportunity, in addition to its mountain of social-media ad revenue.