Pandora Media named founder Tim Westergren as CEO on Monday, but share prices of the music streaming company plunged after the announcement.



"We are pursuing a once-in-a-generation opportunity to create a massive, vibrant music marketplace. We have the audience, the technology infrastructure, the monetization engine and most importantly the right team with the passion and commitment to do it," Westergren said in a statement.



Pandora's stock was down more than 9 percent Monday morning.

"Westergren is now running something completely different than what he created," Wedbush Securities research analyst Michael Pachter said on CNBC's "Squawk on the Street." "Investors don't like it, and they're not going to reward this company until they perform."

Westergren replaced Brian McAndrews, who had been the company's chief executive since 2013.



"I am honored to have been the CEO of Pandora for the past 2½ years, and I am proud of what I and our team of talented and highly passionate colleagues have achieved during this time," McAndrews said.

The company did not say why McAndrews left, but Pachter said "I think that McAndrews probably got bounced for being a little too ambitious."