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

The stock market didn't make very big moves on Friday, with initial modest gains giving way to modest losses as the Dow and S&P 500 posted declines of about 0.2% each. But for Groupon (GRPN -0.61%), United Online (NASDAQ: UNTD), and Financial Engines (FNGN), there was nothing calm about Friday's trade, as all three stocks posted substantial losses.

Groupon plunged 22% as the daily deals turned online retailer reported its fourth-quarter results, including discussion of how costs of acquisitions related to its attempt to recast itself could hurt its bottom line for an extended period of time. With its online-coupon business deteriorating, Groupon has emphasized sales of actual physical goods as having greater potential for growth. Yet, even though Groupon's holiday-quarter results included revenue growth of 20% and adjusted net income that was better than many investors had expected, the company also projected weaker guidance for the current quarter. That left shareholders questioning whether Groupon's turnaround will justify the big jump in share prices that the company enjoyed in 2013.

United Online dropped 12%, giving back about half of its gains from yesterday's session. It looks like it might have taken investors a while to ferret out the complexities of the Internet-specialist's income statement, with the recent spinoff of florist service FTD (FTD) leaving United Online with its Internet service provider divisions and certain social-media elements, including the Classmates service. With no expectations of strong growth, United Online doesn't appear to have as much upside potential as yesterday's almost 30% jump would suggest.

Asset-management services provider Financial Engines fell 11%, again after reporting its fourth-quarter results. Even though revenue grew 27% on a 38% jump in assets under management, Financial Engines gave forward revenue guidance for 2014 that implied a much smaller revenue gain of between 14% and 17% this year. Nevertheless, CEO Jeff Maggioncalda called out the company's new Social Security guidance as a valuable add-on in its suite of informational products for retirement investors. With so many baby boomers in or approaching retirement, Financial Engines has plenty of potential to tap into the demographic boom supporting that aspect of its business.