Stimulus checks are on the way. And with your $600, you could treat yourself to a shiny new piece of tech or stash it in your savings account. Or even better, you could turn that $600 into a whole lot more -- by investing it. But don't forget: You should only invest your stimulus check if your bills are paid and you don't need the money for essentials.

So let's talk about investing. You could put your stimulus check to work by buying shares of companies with strong revenue growth or an especially convincing revenue outlook. And since the coronavirus crisis isn't over, it's a good idea to buy those players that can perform in such an environment in 2021. With this in mind, here are two stocks to add to your watchlist.

An investor pumps his fist in victory as he looks at stock market gains on his tablet.

Image source: Getty Images.

1. Teladoc

Teladoc Health (NYSE:TDOC) is a leader in the telemedicine market. The company provides virtual medical visits to more than 51.5 million members in about 175 countries. The platform offers more than 450 medical subspecialties -- and even advice or second opinions from experts.

Teladoc's revenue soared last year during the coronavirus pandemic, while many doctors' physical offices were closed or operating at lower capacity. And in many cases, patients just preferred the contactless experience of an online visit. Teladoc's revenue in the third quarter ended Sept. 30 climbed 109% year over year. Total visits in the period surged more than 200% to 2.8 million.

It's likely that gains will continue as long as this health crisis continues. But it's also likely gains will continue once it's over. As the U.S. opened for business in June and July after the first major surge of the coronavirus, Teladoc said its visit volumes remained high. In fact, in certain geographic areas, they grew twice as quickly as they did prior to the pandemic.

Teladoc revenue had already been climbing pre-pandemic. Annual revenue has been gaining since the company went public in 2015. It grew at a compound annual growth rate (CAGR) of 48% from that time through the full year 2019. This shows that demand for telemedicine is truly on the rise, and isn't just a trend linked to the pandemic.

Unfortunately, Teladoc hasn't been able to achieve profitability yet. In the most recent quarter, Teladoc reported a loss per share of 43 cents. But earnings estimates for the next fiscal year indicate that profitability is on the horizon.

TDOC EPS Estimates for Next Fiscal Year Chart

TDOC EPS Estimates for Next Fiscal Year data by YCharts.

Last year's merger with Livongo is another element that will quickly boost revenue. Through the deal, Teladoc acquired Livongo's bread and butter -- digital management of chronic diseases. Teladoc predicts the merger will result in $100 million in revenue synergies by 2022.

2. Moderna

In less than a year, Moderna (NASDAQ:MRNA) has transitioned from a clinical-stage biotech company to one selling what might be the world's most sought-after product. The U.S. Food and Drug Administration granted the biotech Emergency Use Authorization for its coronavirus vaccine last month. Moderna is likely to generate billions in revenue in the new year. And considering the global need for a coronavirus vaccine, the company doesn't even have to worry about competition. There's room for several players.

But Moderna isn't resting on its laurels. The success of its coronavirus vaccine provided evidence that the company's messenger RNA (mRNA) technology works in humans. And that's perhaps the biggest victory of all for Moderna. The company uses mRNA to instruct the body to produce a protein from a particular virus. The body then produces the right antibodies to fight off infection.

Moderna is launching three new infectious disease vaccine programs that concern seasonal flu, HIV, and Nipah virus. The company plans to begin phase 1 trials for one seasonal flu candidate and two HIV candidates this year. Moderna also will explore the possibility of combination vaccines, such as a flu/coronavirus vaccine.

These new vaccine programs won't make it to commercialization as quickly as the coronavirus vaccine. Considering the pandemic, researchers and regulators accelerated the process for that product. But Moderna expects to launch another candidate into late-stage testing this year. It will begin a phase 3 trial for its cytomegalovirus (CMV) vaccine. CMV is a common virus that usually doesn't cause symptoms in healthy people, but can be fatal for those with weakened immune systems.

This growth is just beginning

Teladoc and Moderna shares climbed 138% and 434%, respectively in 2020. Right now, Teladoc shares are trading for about $230, while Moderna is trading for about $123. Of course, we can't expect triple-digit share increases every year. But it's reasonable to expect another strong year from these stocks -- and more gains beyond 2021. Demand is rising for Teladoc's at-home services and Moderna's drug products. That spells revenue growth for both. If share performance follows, it's very possible these stocks could turn your $600 into a fortune.

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.