This year has been a banner one for investors. After posting a 6% loss in 2018, the stock market has climbed relentlessly this year, with the S&P 500 gaining more than 33% as of this writing. As impressive as those gains are, some of the year's top growth stocks have done much better -- each gaining more than 100% so far in 2019 -- and they could just be getting started.

Let's take a look at how identity management specialist Okta (NASDAQ:OKTA), Latin American e-commerce powerhouse MercadoLibre (NASDAQ:MELI), and multi-channel commerce platform Shopify (NYSE:SHOP) have all managed triple-digit gains this year, and why they might be just getting started.

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Securing business logins

Over the course of the past decade, the number of large-scale data breaches and hacks has skyrocketed, with nearly 4 billion personal consumer records stolen. This reality makes it tough for employees to keep up with the growing number of account logins and complicated passwords necessary to get through the average workday. Okta (pronounced Ahk-tuh) wants to help ease that pain.

The company's identity management service offers a cloud-based system that handles user authentication for employees, contractors, and customers across a variety of business software and applications -- more than 6,500 in all -- all with a single, secure login process.  

Okta's easy-to-use platform is quickly gaining converts. So far this year, revenue has grown to $419 million, up 48% compared to the prior-year period, while recurring subscription revenue is up more than 50%. Okta's customer base has climbed to more than 7,400 in Q3, up 32% year over year. Even more importantly, Okta's dollar-based retention rate was 117%, showing that existing customers are adding additional services. 

Like many high-growth companies, Okta has yet to produce a profit and is by no means cheap, trading at more than 25 times sales. Shareholders seem to be willing to pay up for Okta's top-line growth, which topped 45% in the most recent quarter. The stock has more than doubled this year, its second consecutive year of triple-digit gains.

As hackers become more sophisticated and digital security becomes more important than ever, the need for Okta's services is only getting started.

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A side hustle takes center stage

MercadoLibre is primarily known for its platform and e-commerce tools that enable a growing number of Latin American merchants to sell their wares online. The company generated net revenue of $603 million in the third quarter, up 70% year over year, and up 91% excluding the results of exchange rates. 

E-commerce sales in the region are expected to grow more than 21% year over year in 2019, but that still represents just 4% of total retail. Compare that to more than 10% in the U.S. and the remaining opportunity is clear. 

One of the roadblocks to even faster growth is Latin America's largely cash-based society, as about 70% of the population doesn't have a bank account, and many don't have a credit card. MercadoLibre recognized this reality early on and introduced MercadoPago, a digital payment service modeled after PayPal, but with a network of convenience stores and other locations that allowed customers to deposit cash. This gave the underbanked a mechanism to pay for online purchases. MercadoPago became so popular, in fact, that it was adopted by other online merchants and eventually by brick-and-mortar retailers as well.

This brought MercadoLibre's payments business to the forefront. In Q3, its total payment volume (TPV) grew 95% year over year to $7.6 billion, while the total number of payment transactions grew 119% to 227 million. Even more importantly, off-platform payments grew to $4 billion, surpassing the payments made on its e-commerce platform, as payments have now become the primary growth driver of MercadoLibre's business.

With triple-digit payments growth and a fertile e-commerce field yet to plow, MercadoLibre's climb has only just begun.

Top view of large storage area in a distribution warehouse interior with goods on the shelf and forklifts

Image source: Getty Images.

A page from Amazon's playbook

Shopify made its bones by providing the platform and tools necessary for merchants to start and maintain an online business. The company supplies more than 70 templates and 3,200 apps that allow sellers to customize the website and user experience to one that's best suited for their customers. Shopify also provides tools that help manage products, keep track of inventory, process payments, and schedule shipping -- regardless of whether the business is online, in brick-and-mortar stores, or at pop-up locations.

The online sales enabler recently took its ambitions to the next level, introducing the Shopify Fulfillment Network, taking a cue from the master of e-commerce, The program allows qualifying merchants to participate, offering a dedicated network of fulfillment centers and featuring smart inventory-management technology. Shortly after its announcement in June, Shopify acquired privately held 6 River Systems, one of the leading providers of collaborative warehouse fulfillment solutions, to jump-start its ambitions.

Merchants are flocking to Shopify's platform, as the company recently announced its user base had grown to more than 1 million merchants in 175 countries. In North America -- its most established market -- about 44% of eligible merchants use Shopify's shipping option. The growth of Shopify Plus -- its platform that caters to enterprise level businesses -- and its ongoing international expansion have supercharged its results in recent months.

For the first nine months of 2019, revenue grew to $1.07 billion, up 47% year over year, though the company is still unprofitable, as it pours all its earnings back into future growth. The stock isn't cheap, selling at 30 times sales, but as e-commerce continues to gain steam, Shopify's win streak will likely continue.

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.