Joe Kennedy, Pandora CEO Resigns, Stock Price Soars 20% After Announcement [PHOTO]

His departure announcement comes on the heels of better-than-expected quarterly sales as the company rallied the past year on improving finances. Shares rose $2.46, or 21 percent, to $14.19 on Friday.

"I reached the conclusion and advised the board that the time is right to begin a process to identify my successor," Kennedy said in a statement.

Fourth-quarter ad revenue rose 51 percent to $109 million, the company said Thursday, sending its shares in after-hours trading up 19 percent to $14.75 after trading as high as $14.80. The gain later retreated after Kennedy announced his departure.

“Over the last nine years I have enjoyed an extraordinary partnership with Joe, working with him to grow the company and build an exceptional team,” Tim Westergren, Pandora Founder and Chief Strategy Officer, said in a statement.

Last year, the Harvard and Princeton-educated executive led a campaign to lobby federal lawmakers to change how its music royalties are calculated. The effort led many music organizations, including the RIAA and ASCAP, to ridicule Pandora.

Pandora, which claims to have 67 million monthly active listeners, said it is the largest radio station in almost every major U.S. market, representing eight percent of total U.S. radio listeners.