Pandora Media (NYSE:P) investors weren't singing a very merry tune last year. The country's leading music streaming service saw its stock plunge 33% in 2014. 

On the surface, seeing a third of its market cap whacked off doesn't seem fair. Pandora is bigger now than it was a year ago. 

There were 76.5 million active monthly users as of the end of September. That's just 5.2% ahead of where it was a year earlier, but listener hours are up 25% to 4.99 billion during the third quarter. In other words, growth is slowing, but those sticking around are spending more time streaming from the site. Pandora's share of total U.S. radio market has grown to 9.09% in September, up from 7.77% a year earlier. 

Pandora's also getting a lot better at monetizing its traffic. Revenue for the third quarter soared 40% over the prior year, fueled primarily by a 44% surge in ad revenue as sponsors are willing to pay more to reach Pandora's mobile users.

Another important factor in Pandora's growth -- and a factor that may have kept sequential user growth in check --  is that it boosted its premium subscription rate in May. New subscribers hoping for ad-free access and other Pandora One perks started to pay $4.99 a month, up from $3.99 a month.

Pandora wasn't the only dot-com speedster to eventually pay the price for a springtime increase. Netflix (NASDAQ:NFLX) was another stock that slipped in 2014 on disappointing user growth during the latter half of the year following a springtime hike.

Unlike Netflix -- which singled out the increase in its most recent call -- Pandora hasn't used the increase as a scapegoat. Then again, unlike Netflix that exists primarily as a premium platform, the vast majority of Pandora's 76.5 million listeners put up with ads and limited song skips to enjoy the service for free.

Battle of the bands
Pandora's success in 2015 will rely largely on what the competition does. Apple (NASDAQ:AAPL) launched iTunes Radio in late 2013, and it's probably not a coincidence that user growth has slowed at Pandora since Apple introduced a similar music discovery service. Despite the limited reach of iTunes Radio -- mobile access is limited to Apple's iOS -- that can change. 

Pandora will also have to contend with Spotify and other on-demand platforms where listeners can actually single out the tracks that they want to hear. Does Pandora embrace that trend by rolling out a new on-demand service? It wouldn't be a surprise since Apple also offers both platforms. 

There's also the potential of international expansion. It's been a couple of years since Pandora entered Australia and New Zealand. There's a world of potential out there, but Pandora has been slow to heed Wall Street wishes for it to be more of a globetrotter. Is 2015 the year that changes?

Analysts see explosive top- and bottom-line growth in 2015. They see revenue climbing by better than 30% with profitability more than doubling. This doesn't mean that usage growth is about to start to accelerate. The active user count will likely stay in the single digits with the revenue growth coming from improving monetization. Will that be enough to satisfy investors that were burned in 2014? Now that Pandora's stock has retreated through 2014 and profits are starting to surge, it should be a healthy year for shareholders if it can keep up with the competition in the booming mobile market.