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 outdoor advertising company Clear Channel Outdoor (NYSE: CCO) plunged as much as 12% earlier in the trading session today after the company reported first-quarter earnings results.

So what: For the quarter, Clear Channel Outdoor reported a marginal boost of 0.1% in revenue to $651 million while losses widened from the year-ago period to $0.14 from $0.03. Both figures fell shy of Wall Street's consensus estimate for a loss of $0.08 on $662.1 million in revenue. The company cited weak international revenue in Europe as the main reason for the drop in earnings. International sales accounted for 56% of Clear Channel Outdoor's revenue in the first quarter.

Now what: This is becoming a nasty trend given that Lamar Advertising (Nasdaq: LAMR) nosedived yesterday after it missed the Street's expectations. But the thing to remember with Lamar is that it missed largely due to an early debt extinguishment. Clear Channel Outdoor's miss was entirely based on sales weakness, which could make it the weakest among its peers. For now, I'm perfectly happy avoiding the company like the plague!

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