The market has had its ups and downs, but some companies have had more ups than downs. In sizing up the universe of investments in order to single out the stocks to keep an eye on this month, I'm narrowing my focus on the ones that have been flying high so far in 2018. 

Shopify (NYSE:SHOP), Axon Enterprise (NASDAQ:AAXN), and Twilio (NYSE:TWLO) have all risen by at least 50% this year. All three are also hitting fresh 52-week highs this week. Let's size up why each stock is rocking right now, and why momentum makes them all stocks to watch in June. 

A police officer wearing an Axon body camera.

Image source: Axon Enterprise.

Shopify

The fast-growing provider of e-commerce solutions is showing no signs of slowing down. Revenue surged surged 68% in its latest quarterly report, and it now powers more than 600,000 online storefronts. 

Shopify's guidance is calling for revenue to decelerate, targeting 52% to 55% growth for the current quarter. However, Shopify has been routinely blasting through its own lowball forecasts. There are plenty of detractors out there, and short interest of 10.6 million in mid-May is a pretty big deal given the stock's three-digit share price. It won't report fresh financials for another two months, but that doesn't mean a short squeeze can't happen at any moment. 

Axon Enterprise

The last time I wrote about the company behind Taser stun guns and its namesake body cameras was 13 months ago, when I singled out the top small-cap stocks to buy that month. The stock has gone on to nearly triple -- up 178% -- so it's fair to say that was a pretty good call.

The stock's been a bottle rocket since changing its name from Taser early last year. The stun guns continue to make up the majority of its sales, but the headiest growth is coming from its sensors and software solutions, which include the Axon cameras and the Evidence.com cloud-based platform that stores all of the collected video footage. Its latest quarter treated investors to 28% in revenue growth, the combination of a 10% uptick in stun gun sales and a 75% surge in everything else. 

Axon bundles its hardware with its storage solutions in five-year deals, giving it growing visibility in its growing business. Axon continues to be in the right place at the right time. Its signature stun guns -- while not perfect -- are gaining momentum as an alternative to handguns in detaining suspects. In a world where some confrontations have escalated, Axon's wearable and dashboard cameras have become essential purchases to verify how incidents played out. 

Twilio

You may not realize it, but the next time you have to reset your Hulu password without leaving the app, or find your Uber Eats driver calling you to announce your grub's arrival, you're probably seeing Twilio in action. Twilio is the top choice for developers when it comes to in-app communications. 

Twilio is coming off of a blowout quarter. Revenue rose 48%, well ahead of the 32% to 34% it was previously targeting. This is only the second time revenue growth has accelerated at Twilio since going public two years ago. Twilio's active customer count has increased by 33% to 53,985 over the past year, and the meaty takeaway there is that revenue growing faster than its Rolodex translates into developers leaning more on Twilio to get their jobs done. 

Rick Munarriz owns shares of Axon Enterprise. The Motley Fool owns shares of and recommends Axon Enterprise, Shopify, and Twilio. The Motley Fool has a disclosure policy.