Fitbit investment spending is driving growth: CEO

Fitbit CEO: Gross margin well within guidance

Fitbit CEO James Park responded to concerns about the company's gross margins Thursday, saying its investment spending contributed to big beats in second quarter revenue.

He said three factors led to gross margin decline: foreign exchange headwinds, increasing capacity for its best-selling product and costs associated with shifting toward products with a higher average selling price.

Park advised investors to look at its operating expenditures as a whole. He explained that Fibit tripled operating expenditures in order to multiply sales by 3.5 times.

"I think we're fairly efficient on opex spending, and in terms of sales and marketing spend[ing], it's not only resulting in short-term benefits. We're really laying the foundation for solid future growth, particularly in international markets," he told CNBC's "Squawk on the Street."

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Shares of Fitbit were down more than 9 percent Thursday despite solid performance in its first earnings report as a public company.

On Wednesday, Fitbit reported adjusted second quarter earnings per share of 21 cents, topping analyst expectations by 13 cents. Revenue grew threefold from the year ago period to $400 million.

However, gross margins declined from 51 percent to 47 percent.

The company's guidance indicated revenue growth would slow and that margins for the next quarter would be slightly lower, Bob Peck, Internet analyst at SunTrust Robinson Humphrey, told CNBC's "Closing Bell" Wednesday.

—CNBC's Jacob Pramuk contributed reporting to this story.