Investing with a long-term perspective doesn't mean you have to buy slow-growing companies. In fact, investors who are in the market for the long haul can more easily stomach the volatility that often comes with owning growth stocks.

To help you track down a few such companies, we asked three Motley Fool writers for their top growth stock recommendations to buy now, and they came back with Repligen (NASDAQ:RGEN), Five Below (NASDAQ:FIVE), and Shopify (NYSE:SHOP). Here's why.

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Biopharma, minus the clinical trials

Maxx Chatsko (Repligen): Investors that make bold bets in the biopharma sector do so in search of eye-popping gains. The problem is, heart-crushing losses stand on the other side of that calculus. That's because biopharma stocks, especially those of development-stage companies, are essentially binary bets on the outcome of clinical trials, most of which end in failure. Wouldn't it be great if investors could capture the growth of biopharma at large without most of the inherent risks? That's where Repligen comes in.

The $1.6 billion company has largely flown under the radar to date, but has rewarded shareholders with 10-year returns of 562%. Repligen accomplished that by staying away from clinical trials altogether. Instead, it has completed a steady stream of acquisitions to become a leading supplier of bioprocess equipment required to purify biologics immediately after production.

It's a sneaky way to piggyback on biopharma growth -- and things are just getting started. In 2017, a record 14 monoclonal antibody drugs (a type of biologic) were approved, joining an estimated 80 such drugs already on the market. There are another 400 in development across the globe. Considering purification is the most cost-intensive and risky step of manufacturing, and that the company's products can be used to manufacture even the smallest quantities of biologics required for clinical trials, the business expects to grow for the foreseeable future. 

After growing 35% from 2016 to 2017, revenue is expected to increase 27% to 32% this year and deliver gross margins in the neighborhood of 56%. Adjusted net income could leap from $27 million last year to $32 million in 2018. With a steady stream of new product launches and increasing value being derived from direct-to-customer sales, Repligen's future remains bright. 

Think young for high growth

Dan Caplinger (Five Below): The retail industry might be the last place you'd expect to find a growth stock right now. Mall-based retailers are facing huge challenges as many of the anchor store chains that help drive traffic to mall locations have resorted to extensive store closings in the face of lack of shopping interest. That's forced smaller retailers to come up with better business models in an effort to survive.

Five Below has come up with what it thinks is an unbeatable combination of favorable traits to appeal to shoppers: inexpensive goods that teen and pre-teen shoppers can afford and want to buy. Even as the retail industry overall has struggled, Five Below has seen impressive revenue growth, with top-line gains of 28% last year and 20%, 22%, and 27% in the three years before that.

After years of little movement, Five Below stock has recently exploded higher as many investors have started to recognize the tween retailer's resilience in a bad market. With a solid e-commerce presence to go with an impressive network of well-placed store locations, Five Below has its finger on the pulse of the youngest generation of shoppers. That could give the chain a leg up for years to come, especially as it hopes to nearly triple the size of its network over the long run.

This company is growing like a weed

Chris Neiger (Shopify): Shopify is an e-commerce platform company that helps businesses of all sizes run their own online store and sell products via social media and through platforms including Amazon.com.

When it comes to growth stocks, it doesn't get much better than Shopify. About 600,000 merchants are now using its platform, up from 243,000 just two years ago. And in the fourth quarter of 2017, Shopify's sales were boosted by 71% year over year. The growth has been sparked in part by its ability to bring bigger (read: more lucrative) companies onto its platform. Shopify ended 2017 with 3,600 high-end Plus customers, including huge companies like Cummins and Ford. Shopify Plus customers pay a premium for the company's services and these sales are helping to boost Shopify's monthly recurring revenue (MRR). MRR from Shopify Plus now makes up 21% of total sales, up from 17% in the year-ago quarter. But wait, there's more. Not only are sales booming, but the company's gross merchandise volume (the value of the transactions processed on its platform) jumped 71% in 2017. 

Management expects full-year 2018 sales to be $980 million at the midpoint, which would be a 45% increase from 2017. Similarly, the sales estimate for first-quarter 2018 is $198 million to $202 million, which would be a nearly 57% year-over-year increase at the midpoint.

Shopify's share price has jumped about 60% over the past year, and while it's experienced some volatility, there's likely more room for this company to run. That's because the online shopping market is still booming and is expected to climb from $385 billion in 2016 to $632 billion by 2020.

Investors should know that Shopify's shares aren't cheap and its stock price is likely to see more dips and pops ahead. But this company is quickly building out its own niche in the e-commerce market and has proved that it knows how to add customers both big and small. If Shopify continues at this pace, stable profitability shouldn't be far behind.