By midmorning, shares had taken off 6% to $37.06.
The internet radio provider said listener hours for February were 1.51 billion, an increase of 9% on the year-ago period. However, that came in at a slower pace of growth than in December and January which both saw increases of 13%.
The company ended February with 75.3 million active listeners, an 11% increase, but less than 13% and 12% in December and January, respectively.
The Oakland, Calif.-based business also said it will discontinue its monthly disclosure of audience metrics in June 2014 (covering May's numbers).
"Given recent changes in the marketplace, including Triton Digital's Webcast Metrics Local recently achieving Media Rating Council Accreditation, Pandora believes advertisers can now access the necessary tools to make accurate side-by-side comparisons," the company said in a statement.
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