This year has tested the resolve of investors like few before it. The unprecedented nature of the coronavirus disease 2019 (COVID-19) pandemic led to historic levels of uncertainty during the first quarter and ultimately wiped away more than a third of the S&P 500's value in under five weeks.

Thankfully, volatility has a way of opening doors for long-term investors. Since bull market rallies inevitably put every stock market crash or correction in the rearview mirror, notable dips in equities are opportunities to put money to work. Investors who bought a basket of innovative companies during the February/March meltdown are likely up on those positions today.

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However, volatility doesn't always bring out the best in investors. Online investing app Robinhood, which is known for offering commission-free trades and gifting free shares of stock to new members, has gained millions of new users in 2020. Unfortunately, many of these millennial and novice "investors" have chosen to chase Wall Street's flavor of the week or downright awful companies. In other words, most Robinhood investors lack the long-term mindset needed to increase their odds of building significant wealth.

The good news is that there's a solution. Robinhood investors are attracted to volatility. Investing in some of the fastest-growing stocks could satiate that desire, while also giving them a chance to build significant wealth over the long term.

Here are three of the fastest-growing stocks Robinhood investors should consider buying now.

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Datadog

The coronavirus pandemic has transformed the traditional office environment as we knew it. With businesses pushing online and into the cloud at an accelerated rate due to COVID-19, software-as-a-service (SaaS) stock Datadog's (DDOG 0.28%) solutions will be in high demand. Datadog's cloud-based SaaS solutions help businesses monitor application performance, better understand user behaviors, and improve knowledge of key business metrics.

Datadog, which is set to release its third-quarter operating results after the closing bell later today (Nov. 10), recorded 68% sales growth in the second quarter. The number of customers generating over $100,000 in annual recurring revenue jumped to 1,015 from 594 in the year-ago period.

Datadog delivered exceptional growth during the weakest quarter for the U.S. economy in decades. It's also seeing its existing clients spend more as they grow. Datadog's solutions are built to expand with its clients, which should yield improved margins over time. 

Unlike a number of other fast-growing cloud-based SaaS stocks, Datadog has also pushed to recurring profitability. Even with the company making acquisitions and spending freely on innovation, there's no concern about full-year losses.

Between 2019 and 2023, Wall Street expects Datadog to grow sales from $363 million to about $1.4 billion, which works out to a compound annual growth rate of 40% a year. That's the type of growth Robinhood investors should chase.

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Innovative Industrial Properties

Marijuana stocks have been the talk of Wall Street over the past week, primarily because of the cannabis industry's green sweep post-Election Day. Unfortunately, Robinhood investors aren't allowed to buy into many of the fastest-growing names in the industry because the Robinhood platform doesn't let members buy over-the-counter-listed stocks. Thankfully, there is still one high-growth pot stock that offers exceptional growth prospects: Innovative Industrial Properties (IIPR -1.03%).

Innovative Industrial Properties, or IIP, is a cannabis-focused real estate investment trust (REIT). It acquires medical marijuana cultivation and processing sites and then leases these assets out for long periods, usually 10 to 20 years. IIP makes its living by collecting rental income, acquiring new assets, and passing along annual rental increases to its tenants.

Innovative Industrial's acquisitions are primarily driving its growth. Having begun 2019 with just 11 properties owned, IIP ended the previous week with 63 properties spanning 5 million square feet across 16 states. The best part is that more than 99% of this square footage is currently leased, with a weighted-average remaining lease length of 16.2 years. Investors can expect highly transparent and predictable cash flow for a long time to come. 

IIP also benefits from its sale-leaseback arrangements. With access to traditional banking services limited for multistate operators, Innovative Industrial acquires properties from cannabis operators with cash and immediately leases these properties back to the seller. These arrangements allow IIP to acquire long-term tenants, while pot companies land much-needed cash.

Though success largely depends on IIP's acquisition activity moving forward, Wall Street expects the company's annual revenue to top $280 million by 2023. For context, it generated just $44.7 million in revenue in 2019.

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Sea Limited

A final fast-growing stock that Robinhood investors can sink their teeth into is Singapore's Sea Limited (SE -0.75%). Sea has a three-part business fully capable of delivering sustainable double-digit or triple-digit growth.

The company's digital entertainment segment is currently responsible for most of its revenue and the bulk of its adjusted earnings before interest, taxes, depreciation, and amortization (EBITDA). Sea is the company behind the hit mobile game Free Fire, which attracted more than 100 million peak daily users during the second quarter. More importantly, its gaming arena has nearly 500 million active users, 10% of whom are paying (up from 8.4% in Q2 2019).

However, the real excitement stems from e-commerce platform Shopee, which targets a number of Southeast Asian countries. This region's rising middle class is quickly becoming accustomed to making purchases online. In the second quarter, gross merchandise volume bought on the Shopee platform jumped about 110% to $8 billion from the prior-year period, with gross orders jumping 150%. This segment could see lasting triple-digit growth even once an effective COVID-19 vaccine is approved. 

Lastly, Sea Limited has ventured into digital financial services. At the end of June, the company had more than 15 million paying mobile wallet users. Though this segment is a relatively small revenue generator for now, it could prove quite lucrative in an underbanked region of the world.

Wall Street is looking for Sea's sales to catapult from $2.9 billion in 2019 to $10.3 billion by 2023, which works out to a compound annual growth rate of 37.3%.