The past 12 months have been generally solid for investors, but some stocks are doing better than others. Earlier this week, I took a look at three stocks that have more than doubled over the past year, but some investments have fared even better.

The Trade Desk (TTD 0.92%)Twilio (TWLO 1.51%), and Glu Mobile (GLUU) have all more than tripled over the past 12 months. Let's go over what has made the three stocks some of the hottest investments over the past year.

The Trade Desk reception area at its headquarters featuring a potted plant behind a license plate with The Desk California etched on it.

Image source: The Trade Desk.

The Trade Desk -- Up 331%

There's big money to be made by disrupting old-school industries, and that's just what The Trade Desk is doing with the advertising industry. The Trade Desk is giving ad buyers a high-tech programmatic platform to allocate marketing budgets, and it's proving as sticky as a hot ad campaign. Customer retention has remained above 95% for 21 consecutive quarters

Growth is accelerating at The Trade Desk, and no matter how often it lowballs its guidance, it seems as if it's always surprising even itself. Revenue soared 56% in its latest quarter, 43% ahead its public forecast. The Trade Desk is also just getting started. Last week, it expanded its efforts to push deeper into China. The world is waiting for its platform that lets algorithm-fueled machines make smarter ad buying decisions. 

Twilio -- Up 254%

There are dozens, if not hundreds, of apps in your pocket, and Twilio is making it easier for them to work. Twilio is the leading provider of in-app communication solutions. From resetting passwords to connecting you with the driver, food, or handyman you just booked online, Twilio lets growing companies stay connected without users ever having to leave the app. 

The number of active accounts on Twilio's platform have soared 31% over the past year, and revenue is growing even faster -- up 77% -- as folks pounding their mobile devices are leaning more on Twilio-enhanced apps. Growth should continue at a heady clip this year. Twilio sees revenue moving 64% to 66% higher in 2019.   

Glu Mobile -- Up 207%

Speaking of apps, Glu Mobile has a pretty good winning streak these days. The casual game publisher behind Kim Kardashian: Hollywood a few years ago is keeping gamers close to their smartphones and tablets with Design Home, Covet Fashion, and Tap Sports Baseball. Those three titles combined for 44% in bookings growth in its latest quarter.

Mobile gamers can be fickle, but Glu Mobile's pipeline is loaded. It's also doing a good job of keeping its existing titles popular as long as feasibly possible. Momentum is on its side, and in this niche, it typically ends in a buyout offer at a hefty premium or a dead end. Glu Mobile will need to know what street it's going down this year.