It's not just the temperatures that are heating up this month. Some stocks have put up scorching returns so far in 2019, and we're only at the midway point.

Roku (NASDAQ:ROKU), JD.com (NASDAQ:JD)Snap (NYSE:SNAP), Zillow (NASDAQ:Z) (NASDAQ:ZG), and Twilio (NYSE:TWLO) have all risen by at least 50% year to date. A lot of the market's biggest winners will undeniably cool down in the second half, but these five names have the right ingredients to keep their rallies going in the month ahead. 

Zillow running on a laptop and smartphone.

Image source: Zillow Group.

Roku 

One of this year's hottest stocks is the pioneer in streaming gadgetry that's working on a more tantalizing second act as a leading software platform for all streaming services. Roku is serving up streaming content to what is now 29 million active users who spend an average of more than three hours a day consuming video content through either Roku hardware or smart TVs powered by Roku's operating system. 

Roku is becoming a staple of more living rooms with every passing quarter, and it's cashing in through the ads it serves on its platform as well as the referral fees it collects when folks sign up for services through its portal. Platform revenue soared 79% in Roku its latest quarter. Roku won't be reporting financial results until next month, but with the stock 14% below the all-time high it hit two weeks ago, bullish sentiment should return ahead of its early August quarterly update.  

JD.com 

Chinese growth stocks got creamed in the second half of 2018, and JD.com didn't help matters much after its CEO was arrested on sexual assault allegations. The e-commerce giant has been on the upswing in 2019 as investor sentiment has turned bullish on China. 

Revenue growth may be decelerating gradually for JD.com -- the year-over-year top-line increase slowed to 21% in its latest quarter -- but profitability is growing a lot faster. JD.com trades at a reasonable 0.6 times trailing sales, and its lofty profit multiple should contract given its heady bottom-line growth.

Snap

Snapchat's parent company is finally out of the doghouse that it's been in since shortly after its 2017 IPO. The social media's user base is finally stabilizing. Snapchat is finally turning its problematic Android app around. A push into proprietary content and mobile gaming should make the app even stickier. 

Losses continue at Snap, but it has consistently been posting narrower-than-expected quarterly deficits. Revenue has been strong as it gets better at monetizing its traffic. Snap reports fresh financial results on July 23, and if it can keep the momentum going, the stock will continue its run as as this year's comeback kid. 

Zillow

There is more to Zillow these days than just its comprehensive real estate listings and its "Zestimates" feature that tracks rough property values. The lion's share of Zillow's growth is coming from its home-flipping business, as its flagship online business has slowed to single-digit revenue growth. 

Zillow sold 414 homes in the first quarter, generating $128 million in revenue. Flipping homes isn't presently profitable for Zillow. It lost nearly $4,000 on each home it unloaded through the first three months of the year. However, this is a business that should be scalable as it ramps up its operations. It's a move that makes sense for Zillow as it's able to reach enough homeowners and prospective buyers to play matchmaker. 

Twilio

The top dog when it comes to in-app communication solutions was one of last year's hottest stocks, and it's picking up in 2019 just where it left off. The stock is nearly a six-bagger since the start of last year.

Many of the hottest mobile apps rely on Twilio to connect two parties to make everything from transactions to support more effective, and Twilio's riding all of those coattails. Revenue growth has accelerated for five consecutive periods, soaring better than 80% in its most recent quarter. Twilio is another one of the stocks on this list that won't be stepping up with a new financial report until early August, but as one of the market's biggest gainers over the past 18 months, it should continue to drift higher if the general market is kind.