Oakland, Calif.-based Pandora has more than 125 million users, and listener growth is doubling on an annual basis. Still, profits elude the company. Fears are growing Pandora may not be profitable for some time. The company competes in the paid radio market with Sirius XM ( SIRI) and Spotify. Pandora noted on a conference call Tuesday that mobile monetization would take place over the next 18 to 24 months, and analysts are worried about the company's ability to execute. Citigroup analyst Mark Mahaney downgraded Pandora, adding to those fears, based mainly off the the company's inability to monetize mobile. Mahaney noted that a good portion of the long thesis is still intact but content costs are constantly rising, and Pandora's inability to generate revenue from its mobile platform (which Mahaney said is over 70% of usage) is a concern. He noted that fiscal year 2013 monetization will be flat, which "blows up the Pandora model." "The broad takeaway for purely ad-based Internet models (especially those that aren't lead-gen or Search based) may well be that the Mobile Transition will be rocky. For a 3-5 year VC timeframe, that's fine. For a 6-18 month Public Investor timeframe, that isn't. Hence, the downgrade...," Mahaney wrote in his note to clients. Mahaney cut the price target to $17 from $25, and downgraded shares to neutral from outperform.