Stocks making the biggest moves after hours: Fitbit, Nutrisystem, Palo Alto & more

A Fitbit display is seen at a Target store in Los Angeles.
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A Fitbit display is seen at a Target store in Los Angeles.

Check out the companies making headlines after the bell Monday:

Fitbit shares dropped more than 11 percent after hours. The wearable technology company reported losses per share of 2 cents and revenues that missed expectations by $18 million, disappointing Wall Street. Guidance for the upcoming quarter and year were both extremely weak, significantly missing estimates once again. The company expects a year-over-year decline in first-quarter revenue of 15 to 20 percent.

The company had a slow holiday season as Apple has become a stronger contender in the wearable business. Fitbit plans to manage down its expenses and expand in the smartwatch category, according to CEO James Park.

Shares of Nutrisystem plunged nearly 28 percent after the bell. The weight loss product and service provider announced earnings per share and revenues that beat analyst expectations, but weak guidance that sent the stock plummeting.

Akorn Pharmaceuticals stock plummeted nearly 38 percent after hours. The pharmaceutical company is under investigation by acquirer Fresenius regarding alleged breaches of FDA data integrity requirements relating to product development. The outcome of the inquiry may affect the merger, says Fresenius.

Palo Alto Networks stock gained more than 5 percent in extended trading. The security company announced growth in revenue as well as EPS and revenues that surpassed expectations. Many analysts were looking at the company's second-quarter billings, which were up 20 percent. The CEO attributes much of this growth to robust customer acquisition.

Tenet Healthcare shares jumped 7.5 percent after hours before settling. The healthcare services company's earnings and revenue beat Wall Street expectations. Its fourth-quarter sales were higher than expected and guidance for the upcoming year is strong.