Think back to February of this year. Growth stocks were tanking left and right, while many investors were rotating to more conservative positions. Some of the highest-flying stocks over the previous months were in negative territory year to date.

But anyone who thought that growth stocks were in for an extended period in the doldrums was mistaken. It didn't take long for a rebound to materialize. Now, the future once again looks bright for this category of stocks. Some are better picks than others, though. Here are three especially promising growth stocks to buy for the second half of 2021.

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Etsy

Etsy's (ETSY -0.48%) shares fell 36% below its highs from earlier this year at one point. Many investors seemed to give up on the stock after the company said that its growth would slow. However, that slowing growth shouldn't have been surprising one bit, considering that Etsy experienced its biggest growth surge ever in 2020 because of the COVID-19 pandemic.

The reality is that Etsy's business remains exceptionally strong. No other e-commerce platform comes close to offering the range of handcrafted products that's available on Etsy. The company now has more active buyers and more repeat buyers than ever before. 

Etsy is also aggressively moving into new markets. Just this month, the company has completed two key acquisitions. It bought Elo7, a top Brazilian online marketplace for handmade products. Etsy also closed on its acquisition of global fashion reseller Depop. 

The Depop deal is especially great because it helps the company more effectively target the $364 billion online apparel market, which is projected to top $540 billion by 2025. With Etsy's market cap around $25 billion right now, the e-commerce innovator should have a clear path for growth in apparel, as well as other retail categories.

Fiverr

Investors were even more despondent about once red-hot Fiverr (FVRR 0.25%) earlier this year. Shares of the online freelancing-marketplace operator sank more than 50% from highs by early May. Still, Fiverr stock was up 24% in the first half of 2021 after making a strong rebound.

Fiverr's business is absolutely booming. The company's revenue doubled year over year in the first quarter of 2021. Over 45% of U.S. businesses are using more freelancers than before the COVID-19 pandemic -- and many of them are turning to Fiverr's platform.

The company continues to expand in two key ways. It's moving into new vertical markets, recently adding data-related services as its ninth vertical focus. Fiverr is also expanding internationally.

Even with its strong growth, Fiverr is still only in its early innings. The company estimates that its total addressable market in the U.S. alone stands at $115 billion. Fiverr's market cap currently is only around $8 billion.

Innovative Industrial Properties

During the growth stock sell-off in late February and early March, shares of Innovative Industrial Properties (IIPR -1.61%) fell nearly 25% below the highs set earlier in the year. Like Etsy and Fiverr, though, IIP came back strong and is now up more than 15% year to date.

Despite the volatility of its shares, IIP's business hasn't skipped a beat. The company is a real estate investment trust (REIT) that's focused on the U.S. medical cannabis industry. And medical cannabis operators are still turning to IIP for sale-leaseback deals that provide them upfront cash (and give IIP a steady ongoing revenue stream).

In the first quarter, IIP's revenue doubled year over year, as earnings soared 122%. The company uses its profits in two main ways -- paying dividends and buying new properties. Both benefit shareholders.

All IIP needs to do to keep the growth coming is to find more medical cannabis properties to acquire and lease out. That shouldn't be too difficult of a challenge. I think this cannabis-focused REIT should deliver solid gains for investors in the second half of the year and beyond.