Shares of Fitbit plummeted 30 percent in extended trading Wednesday after the company reported mixed third-quarter earnings and posted weak guidance for its fourth quarter.

The company reported adjusted earnings of 19 cents per share, in line with Wall Street expectations. Its revenues of $504 million missed expectations of $507 million.

Fitbit also gave weak guidance for its upcoming fourth quarter, and is now expecting revenues between $725 million and $750 million for the holiday season. Analysts forecast fourth-quarter revenues of $985.1 million, according to a Thomson Reuters consensus estimate.

"We continue to grow and are profitable, however not at the pace previously expected," Fitbit co-founder and CEO James Park said. "We are focused on improving the utility of our products and integrating more deeply into the healthcare ecosystem and believe we can leverage our brand and community to unlock new avenues and adjacencies of growth."

The stock has fallen more than 55 percent since its IPO on June 18, 2015, when Fitbit was priced at $20. The stock was trading below $9 in extended trading on Wednesday.