It's been a ho-hum year for investors despite all of the market volatility. The Dow and S&P 500 have inched just a little more than 2% higher in 2018, but there are several stocks that are doing a lot better than that. 

Twilio (TWLO 3.06%)Carvana (CVNA 2.07%), and The Trade Desk (TTD 0.86%) have more than doubled so far this year. The stocks have made their investors a lot of money in 2018, but the big gains don't have to end there. All three companies have catalysts in play that should continue to deliver big gains in 2019. It won't be easy to double again, but let's go over why momentum is on their side.

One of Carvana's earlier multistory car vending machines.

Image source: Carvana.

Twilio: Up 278%

The top provider of in-app communications solutions has had a great year, and things just keep getting better for the stock that has nearly quadrupled in 2018. Revenue growth is accelerating, going from a 41% year-over-year pop in the fourth quarter of last year to advances of 48% in the first quarter, 54% in the second quarter, to a blistering 68% pop the last time out

Twilio makes apps more efficient, and it's doing more than just letting you reset your Hulu password on the fly or having your Uber Eats driver call you to let you know that your chicken parm hoagie has arrived. The number of developers on Twilio's platform has risen 31% over the past year, and they're spending more to make more connections. Its net expansion rate is checking in at 145% for the third quarter, Twilio's best showing in nearly two years.  

Carvana: Up 141%

Selling used cars in new and creative ways continues to pay off for Carvana. Revenue soared 137% in its latest quarter, fueled by a 116% year-over-year surge in the number of vehicles sold. There's more to Carvana than just the multistory vending machines that spit out purchased vehicles. 

The next-gen auto retailer is using high tech and shopper-friendly practices to gain market share and expand its reach. Expansion doesn't come cheap, and that's why Carvana's coming in with its largest quarterly deficit since early 2017. There's a method to the madness, and there's beauty in the scaling process. The gross profit per unit -- a key metric in the auto retailing industry -- has grown from $1,742 to $2,303 over the past year, moving it closer to its goal of $3,000. 

The Trade Desk: Up 174%

Advertisers are learning to trust data-crunching machines to allocate their marketing budgets, and The Trade Desk is leading the way with its algorithmic advertising platform. Revenue shot nearly 50% higher in the third quarter, just ahead of its earlier guidance. Adjusted earnings nearly doubled, blowing through analyst profit targets. 

The Trade Desk beat Wall Street profit expectations by 30% for the quarter, and investors are used to the steady beats. The Trade Desk has landed at least 25% ahead of where analysts are parked with their adjusted income forecasts over the past year. 

Twilio, Carvana, and The Trade Desk are clearly getting the job done in 2018. Momentum is on their side to have a shot at doubling again in the year ahead.