The first half of 2019 has given investors cause for celebration. While the market closed out 2018 with the S&P 500 down more than 6%, Wall Street has come roaring back this year, gaining nearly 19%.

While those gains are noteworthy, there are stocks that have gained far more than the broader market. E-commerce platform Shopify (NYSE:SHOP), Latin American digital seller MercadoLibre (NASDAQ:MELI), and programmatic advertising specialist The Trade Desk (NASDAQ:TTD) have each logged triple-digit gains so far in 2019. Even more importantly, these best-in-class companies are setting the stage for even further gains for investors.

A businessman's finger tracing an upward arrow labeled 2019, with a graph showing uneven but significant growth.

Image source: Getty Images.

Shopify: Up 126%

When it comes to enabling merchants to develop e-commerce capabilities, no one does it better than Shopify. The company not only provides the tools to build a website geared toward digital commerce, but it provides payment services, shipping solutions, working capital loans, point-of-sale systems, and more. Shopify is also increasingly the destination of enterprise merchants, as Shopify Plus provides systems and analytics designed for larger retailers with multistore operations and large numbers of employees. The company is also expanding the features that support international merchants and recently launched a fulfillment network, through which the company will pack and ship merchant goods.

Shopify has continued its strong growth this year, with revenue that beat expectations and grew 50% year over year. Subscription revenue grew 40%, and merchant solutions climbed 58%. The company expects those gains to continue, guiding for 42% year-over-year growth in the coming quarter.

MercadoLibre: Up 118%

While U.S. consumers may not be familiar with MercadoLibre, their peers in Latin America know the company well. It takes the best attributes of Amazon, PayPal (NASDAQ:PYPL), Shopify, and eBay and offers a one-stop shop for merchants conducting e-commerce in the region.

Speaking of PayPal, it was so impressed by MercadoLibre that it recently invested $750 million in the company. "We've been impressed with the digital commerce and payments ecosystem Marcos [Galperin, MercadoLibre's CEO] and his team have built," said Dan Schulman, PayPal's president and CEO.

Why is PayPal so impressed? Consider this: In the most recent quarter, MercadoLibre's net revenue grew 93% year over year in local currency, while payment volume was up nearly 83%. This was supported by user growth that increased 25% year over year, while the number of payment transactions grew by 94%.

The Trade Desk: Up 105%

While not a household name, The Trade Desk is disrupting the advertising industry by providing a platform to manage digital ad campaigns. Ad buyers are no longer forced to embark on lengthy contract negotiations that can take days or weeks. The Trade Desk provides ad buyers with a programmatic system that lets algorithms do the bulk of the work. The platform matches existing ads with their targeted customers by reviewing 9 million ad opportunities each second. 

The Trade Desk is taking advantage of a number of massive opportunities, not only benefiting from the shift to digital advertising but also tapping into the rise of streaming. That resulted in revenue that grew 41% year over year in the first quarter, driven by soaring growth in its connected TV and audio markets, which grew 300% and 270% year over year, respectively. 

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