I love small-cap stocks that are growing fast and have significant runways for future growth. So far in 2021, my two best-performing stocks are both small caps: Silvergate Capital (NYSE:SI) and OptimizeRx (NASDAQ:OPRX). Silvergate stock started off the year priced at $76 and is now flying at nearly $215 a share. That's almost a triple, and the year's not over yet. OptimizeRx is right there with it, shares of the telehealth specialist were selling for $33 back in January but now stand at $90.

Despite this rapid growth, these are both small companies with massive upside. Silvergate has a $5.5 billion market cap and OptimizeRx is at $1.6 billion. Small caps can be risky and dangerous, but if you own the right small caps, your rewards over the long term can be amazing. Here's why I think risk-tolerant investors might want to research these two fast-growing small companies.

A person opens their dress shirt to reveal the Bitcoin logo underneath.

Image source: Getty Images.

1. Bitcoin is sending this small-cap through the roof

The main reason Silvergate is soaring is that it's a bank that's 99% focused on cryptocurrency, and cryptocurrency is super hot right now. In fact, crypto in general and Bitcoin (CRYPTO:BTC) specifically have been soaring for over a year, ever since Square announced the company was making major purchases of the coin, and PayPal Holdings decided to add crypto trading to its app.

Square and PayPal are two of the most prominent companies in the fintech space. These are highly successful financial companies with major investments in crypto trading. This validation of crypto as an asset class has worked wonders for Silvergate Capital stock. Specifically, Silvergate runs its Silvergate Exchange Network (aka "the SEN") to facilitate large financial transactions for the trading exchanges and their institutional clients. So as more people trade crypto, more dollars are held at Silvergate. And the bank profits from all its cash deposits. 

Last year Silvergate stock appeared unproductive for most of the year until Square and PayPal announced their crypto moves in the fall. Since then the share price has dramatically escalated by 1,300%. Of course, the prices of various crypto coins are incredibly volatile. So it stands to reason if that market drops precipitously tomorrow, Silvergate's share price would take a major hit as well.

SI Chart

SI data by YCharts

Nonetheless, there are some strong reasons investors might want to own shares of Silvergate, and not just as a proxy trade for the crypto market. This bank is the top dog and first-mover for banks in the crypto industry. This is no small thing, as crypto markets are in the Wild West stage right now. But have no doubt, financial regulations are coming. And like we've seen in the marijuana market, companies can profit nicely when the government regulates a market. For instance, federal regulations have kept banks out of the marijuana sector, so Innovative Industrial Properties has stepped in and made its investors very happy

One regulatory move might be to require crypto to operate under a banking umbrella. President Joe Biden's Working Group on Financial Markets just issued a report suggesting that only insured banks should issue stablecoins. That makes Meta Platforms' collaboration with Silvergate seem prophetic. Silvergate is going to be the bank for the company's new Facebook coin, Diem, and has exclusive rights to bank customers on its platform. Not bad for a $5 billion company!

Masked doctor shows a masked patient a page on her iPad.

Image source: Getty Images.

2. What telehealth stock is killing it right now?

Doximity (NYSE:DOCS) is a dominant company in the telehealth space. The networking site for doctors has strong financials, including 30% profit margins to pair with its 99% revenue growth. It's a massive winner in this space, which is why shares are trading at 51 times revenues.

On the other hand, the telehealth stock that will make investors the most money might actually be a small-cap player in this space -- OptimizeRx. The stock's five-year chart is pretty impressive.

OPRX Chart

OPRX data by YCharts

So while Doximity is overall a stronger company and a safer stock, a successful tiny stock can make for amazing long-term gains. That's why investors should consider having a few tiny companies in their portfolios, particularly those with upside. And these magnificent returns happen because the stock is starting from a small base.

Both OptimizeRx and Doximity are revolutionizing how pharmaceutical companies and other healthcare players reach doctors. Doximity is a networking site for healthcare professionals. It's an obvious marketing spot for companies that want to reach physicians. And OptimizeRx is even more specialized. The company's platform allows pharmaceutical companies to reach doctors while they are looking at electronic health records online. That's a booming market opportunity as pharmaceutical sales reps are being left in the waiting room. 

While telehealth became the rage during the lockdown, most of us only saw the transformation in the doctor-patient relationship. We were seeing our doctors online instead of in an office visit, so Teladoc Health soared. And when Doximity came public, its stock flew higher as well. As society reopens, short-term players are selling positions in both of these healthcare giants, with the belief that everything will soon go back to normal.

DOCS Chart

DOCS data by YCharts

Although there might be short-term disruption in Teladoc's growth trajectory, it may pay off being bullish on the long-term trend. Also in the case of Doximity (and even more so with OptimizeRx), there likely won't be a "return to normal." Doximity is the best way for doctors to network, regardless of the coronavirus. And OptimizeRx is replacing the pharmaceutical sales call.

While we might soon return to the doctor's office for our visits, in my opinion, the job of a pharmaceutical sales rep has been seriously disrupted by internet marketing to doctors. So companies like OptimizeRx are not hurt at all.

Small is risky, but the rewards are amazing

It's understandable why investors own shares of Square and PayPal and Doximity and Teladoc. These big companies have huge competitive advantages, and their large size indicates how much winning they've already done. Smaller stocks like Silvergate Capital and OptimizeRx feel more dangerous since these companies are relatively unknown. But these stocks are riding the same waves (crypto and telehealth) as those bigger names. And because of their small size and their niche dominance, these small-cap stocks are outperforming the more popular names. These two companies might be worth checking out.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.