If you're looking to turbocharge investing returns, you simply cannot afford to ignore growth stocks. Consider that over the last decade -- a period that spans back to the end of the Great Recession -- growth investing has continued to outperform value.

However, picking great growth stocks is easier said than done, as today's hot stock is often tomorrow's bust. With that in mind, we asked three Motley Fool contributors for stocks with long runways for growth that you may be overlooking. Read on to learn why iRobot (NASDAQ:IRBT), MercadoLibre (NASDAQ:MELI), and Dollar General (NYSE:DG) made the cut.

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A top stock on sale

John Bromels (iRobot): Wall Street didn't like what it saw from robotic vacuum manufacturer iRobot in Q1 2018. After revenue missed analysts' expectations, the market punished the stock, sending shares tumbling 22%. And if you aren't in the know, you might think that was justified. But here's two reasons investors should treat this dip as a buying opportunity.

First of all, iRobot doesn't provide quarterly guidance, so the anticipated revenue number that caused the stock market to panic was more of a stab in the dark. In fact, revenue actually grew by 9% year over year. Management indicated on the earnings call that revenue was in line with its expectations, which should soothe investors' nerves.

The second reason that this dip is a buying opportunity is that it's knocked the company's valuation metrics way down. The company is currently trading at a P/E of less than 30, only the second time that's happened since 2017. And with a massive addressable market (robotic vacuums control only about 23% of the high-end vacuum market), iRobot has plenty of room to grow. The company is also working on a hotly anticipated robotic lawn mower with lots of potential to open up new markets. 

For investors who know enough to look beyond Wall Street's overreactions and into the business' fundamentals, iRobot looks like a great growth stock, especially at this price. 

Tiny boxes and cart on computer with Brazilian flag.

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Despite 100% year-to-date returns, MercadoLibre remains undervalued

Jamal Carnette, CFA (MercadoLibre): Despite the harsh trade rhetoric, Latin American e-commerce provider MercadoLibre is having a great year. As of this writing, shares are up more than 100% year to date and in-the-know investors are starting to take notice. Earlier this year it was heavily reported that PayPal took a $750 million stake in the company, but overlooked in the announcement was the fact that Dragoneer Investment Group chipped in with an additional $100 million investment.

Dragoneer and its founder Marc Stad lack the name recognition of many venture capital firms (by choice), but are a force in e-commerce, fintech, and digital payments. Against that backdrop, it's understandable that the firm views MercadoLibre as a viable investment, as e-commerce will only continue to grow in Latin America as internet penetration and disposable income increase.

Perhaps more exciting for Dragoneer is MercadoLibre's digital payments solution MercadoPago, which has grown in scope from a simple transaction facilitator of its e-commerce platform to something more valuable. In the fourth quarter, "off-platform" payments exceeded those made on the platform. This high-growth business is a significant portion of MercadoLibre's total revenue, 39% in the recently reported first quarter.

Mercado Pago is quickly becoming the de facto money transfer service in Latin America. If it succeeds in this regard, the company remains undervalued and has a long runway for continued growth.

Pennies on the dollar

Rich Duprey (Dollar General): The deep-discount end of the retail market remains a highly successful one. Where many retailers that survived the wave of bankruptcies that have swept over the industry in the past few years are still struggling, the dollar stores continue to thrive.

Dollar General may be the best of the bunch. After losing to rival Dollar Tree several years ago in the bidding war for damaged competitor Family Dollar, it threw itself into expanding its own base of stores and investing in its business. It's continuing that cycle of investment and that could represent opportunity for investors.

The deep discounter is spending $50 million this year on a handful of initiatives that will see it bring a lot of its supply chain business in house, add more fresh produce to its shelves, and expand technological improvements.

Wall Street is forecasting an increase of only 2% in earnings this quarter, to $1.39 per share, and management has said its performance will be weighed down by its initiatives. Although they ought to pay off in the long run, if they affect profits and margins as expected, investors may take a dim view of the stock.

That will give savvy investors a chance to pounce on the opportunity. Dollar Tree is still struggling to integrate Family Dollar, and the upgrades being made by Dollar General ought to position it well ahead of the pack.