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's happening: Shares of Yelp (NYSE:YELP) were down almost 21% as of 1 p.m. Friday despite the online business review specialist's better-than-expected fourth-quarter results.

Quarterly revenue climbed 56% year over year to $109.9 million, which resulted in adjusted net income that more than doubled to $18.9 million, or $0.24 per share. Adjusted earnings before interest, taxes, depreciation, and amortization rose 150% to $25.1 million. Analysts, on average, were looking for earnings of just $0.07 per share on sales of $108.4 million.

For the current quarter, Yelp expects revenue of $114 million to $116 million, or growth of roughly 51% at the midpoint, with adjusted EBITDA of $19 million to $21 million. That's roughly in line with Wall Street's outlook for first-quarter earnings of $0.03 per share on sales of $115 million.

Finally, for full-year 2015, Yelp sees revenue of $538 million to $543 million, or growth of 43%, with adjusted EBITDA of $100 million to $103 million. That's ahead of analysts' consensus for sales of $538 million and earnings of $0.40 per share.

Why it's happening: So why the drop in share price? Though Yelp's average monthly unique visitors in the fourth quarter rose 13% year over year to 135 million -- bolstered by a 37% increase in mobile visitors, to 72 million -- investors are concerned because that also represents the company's first-ever sequential drop in total visitors, down from 139 million in the prior quarter.

But this shouldn't be entirely surprising. Management reminded investors the slowing year-over-year growth in the fourth quarter is consistent with seasonal trends, and it expects traffic to resume sequential growth in the first quarter. What's more, it's no surprise that growth in Yelp's core U.S. business would eventually wane, and the company's international sites still generated just 3% of overall revenue in the fourth quarter. Management also noted that, consistent with previous comments, it expects to need years to build the necessary traffic and visitor base to effectively monetize its relatively new foreign sites -- which, by the way, in 2014 contributed about 2 million of Yelp's 71 million cumulative reviews. All things considered, it appears Yelp's long-term story remains firmly intact.