LinkedIn (LNKD) now has 300 million members on its online professional networking platform. No doubt, the large user base has turned into a valuable asset, with the company’s market value at $21 billion. But despite this, the announcement may not mean much for investors. Consider that in today’s trading LinkedIn stock is only up about 1%.

So why isn’t the 300 million user number a boost? Well, one reason is that LNKD is only counting registered users. It doesn’t indicate how often they come back to the site or click on the mobile app, which would be a metric like MAUs (monthly active users). If anything, LNKD has been desperately trying to ramp up engagement with premium content, SlideShare (an online platform for presentations) and the Pulse mobile newsreader.

From a monetization standpoint, it may be tough for LNKD to monetize the new users, as it appears that many of them are from outside the U.S. (about 67% of the total base). All in all, it will take time to build the infrastructure for services like recruiting. For example, the No. 2 segment for LNKD is India and No. 3 is Brazil.

And finally, it is unrealistic to believe that LNKD can reach the massive user levels of Facebook (FB) and Google (GOOG). Let’s face it, these services appeal to broad swaths of consumers, whereas LNKD is focused mostly on the narrower segment of business professionals. According to the company, the “global workforce” is about 3.3 billion people while the total population is 7 billion. So at best, LNKD is only targeting half the market that FB is.

Yet there are still some important nuggets from the LNKD announcement:

• In 2014, mobile is expected to be responsible for more than 50% of global traffic. A key will be leveraging partnerships, such as with Apple (AAPL), Nokia and Samsung.
• LNKD has expanded its presence in China by launching its new Simplified Chinese site. The firm also created a joint venture with Sequoia China and CBC to seek out business opportunities. The goal is to get 140 million Chinese professionals in the LNKD network (although, there was no timetable announced).
• LNKD is no longer just about the technology industry — the No. 2 profession is healthcare and No. 3 is actually construction

While all this is great, there are still worrisome issues for LinkedIn stock. For the most part, the company has been slowing down. When it reported its latest earnings, the forward guidance for Q1 was $455 million to $460, which was below the Street consensus of $471.3 million. As for the full-year forecast, LNKD put out an estimate of $2.02 billion to $2.05 billion. But analysts were looking for a more robust $2.16 billion.

The result has been tough on LinkedIn stock. Since reaching $223 in February, LinkedIn stock is now sitting around $177. Part of this has been from the plunge in social stocks, as seen with Twitter (TWTR), Facebook, Yelp (YELP) and Pandora (P). But the drop in LinkedIn stock may also be due to concerns that the company may have troubles ginning up growth.

If so, this could mean even more problems for the stock. After all, the valuation is still at a lofty level — about 13 times sales and 71 times forward earnings. Such metrics are out-of-whack for a company that is decelerating. So while LNKD service may be popular and useful, it may not be enough to justify the current stock price.

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.