Pandora Media Inc. said the number of hours that listeners tune into its Internet radio service rose 15% during the fourth quarter, helping push its revenue up by a third. Shares fell 21% to $14.60 in recent after-hours trading despite profit growth of 37% as revenue missed expectations and Pandora's outlook for the first quarter and 2015 missed Wall Street's views. For the latest period, the Oakland, Calif., company reported revenue of $268 million, below company expectations for between $273 million and $278 million. Advertising revenue grew 36% to $220.1 million, while local advertising sales soared 90% to $49.9 million. For 2015, Pandora forecast revenue of $1.15 billion to $1.17 billion, while analysts polled by Thomson Reuters expected $1.21 billion. For the first quarter, the company forecast revenue of $220 million to $225 million, below analysts' expectations for $244 million. Pandora's third-quarter financial results fueled concerns about a slowing pace of user growth as well as rising content costs. During the latest quarter the number of listener hours rose to 5.2 billion from 4.54 billion a year earlier. The number of active listeners reached a total of 81.5 million at the end of 2014, an increase of 7% from a year earlier. Overall, Pandora reported earnings of $12.3 million, or six cents a share, compared with a year-earlier profit of $9 million, or four cents. Excluding items such as stock based compensation, earnings were 18 cents. The company expected per-share earnings of 17 cents to 19 cents.