Investors are digging that new stock smell on Wall Street this year. We've seen 80 stocks hit the major U.S. exchanges in 2019, and nine of them have already more than doubled. Shareholders who got in early on those debutantes are sitting pretty right now, but some of the winners are faring even better than the others.

Beyond Meat (NASDAQ:BYND), MMTec (NASDAQ:MTC), and ShockWave Medical (NASDAQ:SWAV) are the biggest gainers among the IPO class through the first half of the year. They're the only three 2019 newbies to have more than tripled in value off their initial price tags. Let's see what's making these fresh market darlings click. 

Beyond Meat plant-based burger patties packaged for retail.

Image source: Beyond Meat.

Beyond Meat: up 543%

It may seem odd that this year's hottest IPO is a distributor of veggie burgers, but it's hard to argue with Beyond Meat's torrid growth. Revenue soared 215% in its first quarter as a public company, as restaurant chains continue to add its plant-based namesake burger to their menus and more supermarkets stock the retail version of its products. 

Bears think the stock's overvalued, which a fair shot since it's trading at more than 85 times trailing revenue. Bulls will counter that looking back isn't a fair measuring stick for a fast-growing company, as Beyond Meat's top-line multiple drops below 50 if we go by its guidance, calling for at least $210 million in revenue for all of 2019. 

A thin float and freakishly high number of short positions relative to that float have made the stock volatile, and it will remain that way. The stock may seem to be due for a breather in the second half of 2019, but with so many people thinking exactly that, it becomes much easier said than done. 

MMTec: up 321%

This year's second biggest gainer is an obscure Beijing-based company that had the misfortune of going public in early January, just as investors were spitting out Chinese growth stocks. MMTec had to settle for an offering at $4, and it has more than quadrupled, with its stock price in the mid-teens.

MMTec has developed products that let Chinese-speaking hedge funds, mutual funds, and other investing groups engage in global securities market transactions. This stock is risky, largely because the company is just getting started. The company was founded early last year, and it didn't start generating revenue until last summer. MMTec still has a lot to prove, but the stock has moved higher largely because the climate for Chinese growth stocks has improved since its depressed IPO nearly six months ago.

ShockWave Medical: up 236%

Finally, we have ShockWave Medical aiming to improve the prospects of patients suffering from cardiovascular diseases. True to its name, the market darling's intravascular lithotripsy platform emits sonic waves that travel through arteries to break up calcium deposits.

Revenue soared 450% in its first quarter as a public company, a pace more than double Beyond Meat's torrid top-line surge. ShockWave's guidance calls for 169% to 194% in revenue growth for all of 2019. ShockWave Medical is still small, but bulls believe its platform can have applications in the larger markets for coronary artery disease and aortic stenosis in the future.