What: Shares of Pandora Media (NYSE:P) were down 17.4% as of 11:00 a.m. ET Friday after light forward guidance and an aggressive long-term strategic growth plan overshadowed the music streaming company's solid fourth-quarter 2015 results.

So what: To put today's drop in perspective, it's worth noting Pandora stock closed up nearly 9% on Thursday after The New York Times reported the company might be in talks to sell itself to a number of unnamed suitors. When asked about the report during the Q&A portion of yesterday's conference call, Pandora CEO Brian McAndrews predictably stated, "We don't want to comment on rumors."

Meanwhile, Pandora announced fourth-quarter revenue grew 25.4% year over year to $336.2 million, and adjusted earnings before interest, taxes, depreciation and amortization dropped 43.4% to $24.8 million. Pandora's guidance called for lower revenue of $325 million to $330 million and higher adjusted EBITDA of $25 million to $30 million. However, adjusted EBITDA would have been $27.3 million (in line with expectations) excluding the negative impact of Pandora's recently closed acquisition of Ticketfly. 

Pandora also saw monthly active listeners fall slightly on a year-over-year basis to 81.1 million but also increase 3.8% from last quarter to 78.1 million. This sequential increase should help appease investors' concerns from last quarter over whether the negative impact on listener growth of Apple Music, which launched to much fanfare this past June, is indeed temporary as McAndrews asserted three months ago.

On the bottom line, that translated to a GAAP net loss of $19.4 million, or $0.09 per share. On an adjusted basis -- excluding stock-based compensation and acquistion expenses -- Pandora generated net income of $10.2 million, or $0.04 per diluted share.

Now what: But what really raised eye brows across Wall Street was Pandora's aggressive plans for the future, which will start with $345 million in 2016 investments aimed at scaling infrastructure and building new lines of business. Most significantly, that includes $100 million in product development costs primarily driven by its acquisition of assets and talent from on-demand music specialist Rdio last month, as well as $120 million for developing and launching new music services to accelerate revenue starting in 2017. In particular, Pandora believes it can build a $1.3 billion subscription business over the next five years by launching new product tiers -- an estimate "conservatively" based on converting 10% of its current U.S. audience to these new tiers.

As a result, Pandora expects current-quarter revenue of $280 million to $290 million, which should translate to an adjusted EBITDA loss of $75 million to $65 million. For full-year 2016, Pandora expects revenue of $1.40 billion to $1.42 billion and an adjusted EBITDA loss of $80 million to $60 million. Analysts, on average, were anticipating full-year revenue near the high end of that range and 2016 adjusted earnings of $0.06 per share. 

In the end, it's likely not so much the light guidance throwing off investors today but rather the bold nature of -- and uncertainty created by -- Pandora's investment plans going forward. Don't get me wrong: If Pandora succeeds, it should emerge a much stronger, more profitable business for it. But this plan undeniably creates risks with which some investors admittedly may not be comfortable.

Then again, with last quarter's painful 40% post-earnings drop in mind, it's not as though Pandora investors are unaccustomed to volatility. But if one thing is sure, it's that the next few years should be exceedingly interesting for Pandora Media.

Steve Symington owns shares of Apple. The Motley Fool owns shares of and recommends Apple and Pandora Media. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.