No long ago, Wall Street considered Facebook (FB) to be a washed up has-been. But Facebook’s fourth-quarter report makes the company look more like a breakout startup.

Since the report, investors can’t seem to buy enough shares, with FB stock up about 16% to $62 in today’s trading. But interestingly enough, there may be even more upside — say 18% or so. That’s is the call from Stifle analyst Jordan Rohan, who makes a pretty good case for FB stock.

FB Stock Strengths

First of all, Facebook has made a successful transition to mobile, with about 53% of advertising revenues coming from this source. Other companies, like Zynga (ZNGA) and Yahoo! (YHOO), have struggled with the move to mobile.

Jordan also points out that FB has posted six consecutive quarters of overall ad growth. That growth hasn’t just been about making better apps (although that has certainly been helpful for FB stock) — the company has also built an amazing platform to monetize mobile. For example, FB has worked hard to build an ad platform that is easy to use and leverages the treasure trove of data.

Facebook has also placed a lot of focus on metrics. This is critical because, in the early stages of a new technology, advertisers want to get some proof that it works. And so far, it looks like mobile ads are a slam dunk. As Facebook COO Sheryl Sandberg said on the conference call, the average return on news feed ads was an incredible 8x.

According to Jordan, the monetization machine will provide a hefty boost for FB stock. In light of the projected strong growth, he has computed earnings per share of $2.07 for 2016. Assuming a multiple of 35x, FB stock should trade at about $72.

FB Stock Challenges

But investors should take Jordan’s analysis with some grains of salt. Let’s face it, he’s looking at a much longer time frame than most. As seen with apps like SnapChat or Pinterest, there will inevitably be new operators that will attempt to take away users from Facebook.

But it also looks like Black Friday was a key part of the momentum for Facebook’s Q4. However, that raises the question of what the catalyst will be in Q1 and Q2 As mobile quickly matures, it may be subject to seasonality.

Another factor that could weigh on FB stock is the nagging teen problem. The company did not provide any details on this matter on the conference call. But if teens are moving away from the social network, that could pinch revenue growth.

FB Stock Outlook

Granted, FB definitely had an impressive performance in Q4 and has done just about everything right when it comes to mobile. But Wall Street is already factoring this in, as FB stock has gotten much richer (the forward price-to-earnings ratio is a hefty 41X). Besides, mobile is still in the early years, and investors should expect lulls.

So for now, it’s probably best to be cautious. All in all, it could get tougher for FB stock to crank out future gains.

Tom Taulli runs the InvestorPlace blog IPO Playbook. He is also the author of High-Profit IPO Strategies, All About Commodities and All About Short Selling. Follow him on Twitter at @ttaulli. As of this writing, he did not hold a position in any of the aforementioned securities.