Do you know what the world's most successful investors do when their favorite growth stocks are down? 

The latest disclosures institutional investors made regarding the last three months of 2022 recently became available, and there's a clear trend. Billionaire money managers were eager to buy more shares of their favorite businesses despite their poor stock market performance.

Billionaire fund managers bought millions of shares of these three stocks in the fourth quarter. Read on to see why they're buying them hand over fist despite a bear market.

Amazon

The first exceptional growth stock that's attracting attention from multiple billionaire money managers is Amazon (AMZN -0.01%). Jim Simons added more than 3 million shares of the e-commerce and cloud computing giant to Point72 Asset Management's portfolio in the fourth quarter.

Shares of Amazon fell hard last year in response to a bottom line that sank deep into negative territory. The company more than doubled the size of its North American fulfillment network to meet surging demand during the lockdown phase of the pandemic.

The company pushed a little too hard on the accelerator in 2020 and 2021, but demand is quickly catching up with capacity. The company's North America segment shrank its operating loss from $2.6 billion during the first nine months of 2022 down to a loss of just $240 million during the fourth quarter.

Of course, Amazon's a lot more than just an e-commerce company. Operating income from its cloud computing business rose 23% in 2022 to $22.8 billion. This isn't the company's only fast-growing, high-profit-margin venture, either. Net sales from its advertising business grew 23% year over year to reach $11.6 billion in the fourth quarter.

Dexcom

Israel Englander and Millennium Management bought over 2.6 million shares of Dexcom (DXCM -0.24%) in the fourth quarter of 2022. This is a specialized medical-device maker that develops a popular line of continuous glucose monitoring (CGM) devices for people with diabetes.

The company's new lead product, Dexcom G7, earned regulatory clearance in the EU last March. This helped international sales soar 28% in 2022.

In the U.S., where the company records around three-quarters of total revenue, the FDA granted G7 clearance last December. There are more than 37 million Americans living with diabetes, and keeping their blood sugar concentrations in an ideal range greatly reduces their risk of hospitalizations.

Dexcom's CGMs aren't cheap, but they're a lot less expensive than a stay in a hospital. Strong demand from cost-conscious healthcare plan sponsors with millions of diabetic patients to monitor could drive sales through the roof.

Good stocks to buy now?

Both of these businesses are expecting top-line revenue to grow at double-digit percentages this year. With a diversified operation that can produce heaps of cash, following Englander into Amazon looks like a smart move at its present valuation.

Amazon shares have been changing hands for just 29.5 times 2021 earnings. That was an exceptional year, but this is also a much bigger business now than it was then. Investors who buy the stock at recent prices have an excellent chance to come out ahead over the long run.

The U.S. launch of Dexcom G7 will make 2023 a big year for the company, but there's already a great deal of success baked into the stock. With the stock trading at 110 times forward-looking earnings estimates, investors who buy Dexcom now could suffer heavy losses if sales don't accelerate and continue soaring for several more years.

Another CGM from Abbott Laboratories earned FDA clearance last May. Abbott's CGM has a long lead, and it's also significantly smaller. Stiff competition from Abbott could make it hard for Dexcom to meet the lofty expectations the market has placed on it. With this in mind, it's probably best to keep Dexcom on a watchlist for now.