The stock market has rewarded investors with significant returns over the past year, and that raises the risk that a reckoning is coming. But let's not panic; any sell-off in stocks could be an opportunity to buy top growth stocks in long-term portfolios. There are plenty of attractive stocks to consider, but the three stocks I'm targeting are Atlassian Corporation (NASDAQ:TEAM), Teladoc Health (NYSE:TDOC), and Zendesk Inc. (NYSE:ZEN). Read on to find out how buying these stocks in a market tumble could pay off.

Cashing in on collaboration

More than 120,000 companies already use Atlassian's cloud-based collaboration software to connect workers all over the globe, but its addressable market is the Fortune 500,000, and that suggests there's plenty of opportunity to boost sales by adding new accounts and expanding existing relationships.

A man in a shirt and tie with a dream cloud above his head containing $1 bills.

IMAGE SOURCE: GETTY IMAGES.

The company spends more than twice as much on research and development as on sales and marketing every quarter, and as a result, it has established a loyal following, particularly in IT, where collaboration tools are especially useful.

Its customer-centric focus -- one motto is "don't #@!% the customer" -- has paid off with considerable growth that I believe will continue to reward investors. Revenue was $874 million last quarter, and this year, management thinks it could reach $1.18 billion. Importantly, the company's cost consciousness is boosting the bottom line as revenue increases. Last fiscal year, adjusted earnings per share were $0.49, but this fiscal year, management is targeting $0.78.

Speaking of management, Atlassian's founders remain at the helm, and since they own more than 50% of the company, they're nicely aligned with individual shareholders' long-term objectives.

The big knock against Atlassian is its valuation, because it trades at about 78 times forward earnings. Nevertheless, this is one of my favorite growth stocks to buy on a crash, because connecting workers to boost productivity will remain critical, regardless of the stock market's whims and whispers.

Dialing in on telemedicine

Serving an increasingly larger and longer-living population with prompt, inexpensive primary care is one of the biggest challenges in healthcare. More than 60 million people in the U.S. have inadequate access to a primary care physician, according to National Association of Community Health Centers, and those with access to one could arguably be better served than they are today.

There's no magic bullet to increasing access and reducing cost, but the widespread adoption of telemedicine, or telehealth, could be one solution. If so, then Teladoc could benefit nicely, because it's the leader in this emerging market.

Last year, it completed nearly 1.5 million telehealth visits, up from 952,000 in 2016, and it entered 2018 with more than 10,000 payers providing access to its services to more than 23 million people. Its momentum isn't slowing, either. In Q2, sales jumped 112% year over year to $94.6 million, and patient visits increased 72% to 533,000. A good chunk of its growth is from acquisitions, but its 39% organic growth rate in the past year is nothing to sneeze at.

Importantly, the company is not close to maximum capacity. Teladoc believes telehealth can treat 417 million of the 1.25 billion outpatient visits to care providers annually in the U.S., and that means it has a massive market opportunity. Last year, it averaged 7,000 visits per day, but it believes it can provide the same level of service for up to 50,000 visits per day and that its platform can handle up to 100 million members. 

Obviously, there's no guarantee Teladoc will ever get that big, but I think the demand is there to support years of double-digit growth. If I'm right, then its revenue in 10 years will be much higher than the $405 million to $410 million it expects to report this year.

Four young professionals using electronic devices in an office.

IMAGE SOURCE: GETTY IMAGES.

Connecting with customers

Removing bottlenecks that frustrate customers is key to building organizations that benefit from repeat business, so companies are increasingly embracing Zendesk's cloud-based customer service tools.

Founded in 2007, Zendesk provides solutions, including Zendesk Support and Zendesk Chat, that streamline customer interactions, regardless of how customers want to communicate or where companies are located. Last year, 47% of the $430 million it reported in revenue came from outside the United States.

Most of the 118,000 paid accounts it claimed at the end of 2017 were small to mid-sized businesses, but it's starting to target larger companies successfully, too. For instance, it closed "60% more deals with an average contract value of $50,000 or more compared to a year ago" in Q2 2018 and that helped revenue grow 39% year over year to $141.9 million in the quarter.

This year, the company expects to deliver sales of at least $582 million, and its long-term target is for revenue of $1 billion in 2020. That's a heady target, but if it can deliver on that goal, the company could make the jump to consistent, shareholder-friendly profitability. Its net loss was $0.03 per share in Q2 after adjusting for share-based compensation expenses.

The common threads among all three of these companies is that each is disrupting large markets, producing sales growth, and focusing on customers. I suspect shares in Atlassian, Teladoc, and Zendesk could drop significantly if the market falls, so these stocks won't be right for everyone. Overall, though, I think they're smart additions that will pay off over the long haul for growth investors.

Todd Campbell has no position in any of the stocks mentioned. His clients may have positions in the companies mentioned. The Motley Fool owns shares of and recommends Atlassian. The Motley Fool recommends Teladoc and Zendesk. The Motley Fool has a disclosure policy.