Finding stocks that can double their value is something of the holy grail of investing. Riding a stock to 100% gains often takes years or even decades, though in rare cases it can happen much faster. While some would simply take their winnings and go, in-the-know investors will want to determine what drove those gains, because in some cases the stock will still have room to run and remain a worthwhile investment.

With that in mind, let's look at three companies that have enjoyed triple-digit gains so far in 2019 and may still have room to grow: streaming pioneer Roku (NASDAQ:ROKU), e-commerce car seller Carvana (NYSE:CVNA), and digital advertiser The Trade Desk (NASDAQ:TTD). Let's look at each to see why this year's outperformance might be just the beginning.

A Roku TV showing shortcuts to streaming services.

Image source: Roku.

Roku: Up 416%

It's easy to see why investors might be doubtful about the growth prospects for a stock that's grown nearly fivefold in 11 months, yet the trend that's driving those gains is just getting started. While Roku is widely known for its streaming video devices, the company banks most of its revenue from its advertising business. As consumers increasingly move from traditional broadcast television to streaming platforms, Roku provides data that helps advertisers reach only those consumers that are in the market for their products or services.

This has been Roku's recipe for success. The company's platform revenue -- which includes advertising, The Roku Channel, and its connected TV operating system (OS) -- has grown 81% year over year during the first nine months of 2019 and shows little signs of slowing. Additionally, Roku's OS is the platform of choice for many manufacturers and can be found in 1 in 3 smart TVs sold in the U.S. -- and the company is just now beginning its European expansion

As more people cut the cord and the adoption of streaming accelerates, Roku is carving out a niche that will bear fruit for years to come.

Carvana vending tower in Charlotte

Image source: Carvana.

Carvana: Up 178%

You might be surprised to find a car dealer on this list, but Carvana has turned the industry on its head by becoming a leading e-commerce platform for buying and selling used cars. By bringing technology to the space and consolidating a fractured marketplace, Carvana has produced 23 consecutive quarters of triple-digit revenue growth. That's right: year-over-year growth of more than 100% for 23 quarters running. 

There are a host of factors helping drive Carvana's gains. Not only did the number of cars sold during the quarter increase 83% year over year, but the company has also been making more money on each sale, as gross profit per unit grew to $2,963, up from $2,263 in the prior-year quarter. The company has also added nine new markets in its most recent quarter, bringing the total to 146, now covering about 66% of the U.S. population. Carvana plans to eventually reach 90% of the country.

There are plenty of reasons to believe that Carvana will continue to prosper -- even after soaring this year.

Two hands touching digital globe showing various consumer advertising touchpoints

Image source: Getty Images.

The Trade Desk: Up 121%

Back in January, I named The Trade Desk my highest-conviction stock for 2019, and it has certainly lived up to the hype. The company sits at the intersection of a powerful and growing trend.

The programmatic advertising specialist uses high-speed computers and complex algorithms to not only match ad inventory with available slots, but also to place the ads in front of the right consumers -- and Trade Desk is good at what it does. While programmatic advertising is growing at 20% -- four times the rate of the overall ad industry -- so far this year, Trade Desk increased revenue 54% compared to the prior-year period.

This means the company is stealing market share from its larger rivals, like Facebook and Google, a division of Alphabet. Trade Desk doesn't capture any personal data, giving it a huge advantage as regulatory agencies across the world clamp down on data privacy.

Several areas of Trade Desk's business are notable for their growth. Mobile video advertising grew 50% year over year, while in-app ads grew 58%. Other segments are generating even more robust results. Connected TV ads soared 145% year over year, while audio advertising jumped 160%.

The combination of the right technology in the right place at the right time is driving Trade Desk higher, and the company will be a force to be reckoned with in the years to come.

The usual disclaimers

By now, investors have no doubt heard the old adage that past performance doesn't guarantee future returns. Additionally, two of these high-growth companies -- Carvana and Roku -- have made the decision to forego profits and continue to plow all of their resources into future growth. There's also the matter of frothy valuations. Carvana, Roku, and Trade Desk have price-to-sales ratios of 3, 16, and 17, respectively, while many investors consider a reasonable metric to be between 1 and 2 -- so they're by no means cheap.

None of these factors have stopped these companies from being top performers this year, and for investors willing to pay up for the astonishing growth rates outlined above, these highfliers likely still have ample gas in the tank.