Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Zynga (Nasdaq: ZNGA) have fallen by as much as 12% today to all-time lows on continued fears of a slowdown in social gaming, sparked by bearish analyst comments.

So what: Cowen & Co. analyst Doug Creutz says that daily average unique users have fallen by 4.8 million -- to 54.2 million -- over the past month, indicating that Facebook's (Nasdaq: FB) desktop platform is past its prime. He believes that the platform has hit a "negative inflection point" as gamers migrate toward mobile platforms.

Now what: On the other hand, Zynga is aggressively trying to move into mobile gaming, but for now still relies on Facebook for the vast majority of sales. Just as mobile is a weak spot for Facebook, it's also one for Zynga. Creutz notes that this is the second, consecutive, significant, sequential drop in daily users, which doesn't bode well for its future prospects. That figure above represents an 8.2% plunge in daily users.

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Fool contributor Evan Niu holds no position in any company mentioned. Click here to see his holdings and a short bio. The Motley Fool owns shares of Facebook. The Motley Fool has a disclosure policy. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days.