Facebook and Twitter Inc, which will soon raise $1 billion or more in this year's most-anticipated initial public offering, may also increasingly grab smaller customers from Google.

And then there is Motorola - which only recently began selling the vastly customizable Moto X smartphone in a bid to reverse years of losses and finally generate growth. Sales numbers are not yet available but reviews generally dismiss the device's chances of displacing, say, the iPhone.

Motorola, acquired by Google in 2012, racked up a loss of $218 million before items in the third quarter, more than four times the $49 million it lost a year earlier.

"While we acknowledge that most investors will look at Google more positively following this quarter, we think that over time issues such as margin erosion, competition and capital intensity will eventually impact the stock," Wieser said, explaining his below-average price target.

A study in contrasts

Google's Friday rally stemmed in part from investors' focus on Facebook and its own increasingly successful efforts to sell advertising on mobile devices. Google stock had gained just 26 percent this year, while Facebook's has almost doubled.

Google and Facebook, which is expected to report its third-quarter results on Oct 30, also stand head-and-shoulders above the likes of Yahoo. The once-dominant Internet portal this week reported a tepid quarter, losing market share in display and search advertising.

Facebook rose 3.6 percent to $54.08 on Friday, while Yahoo was up 2 percent at $33.40. Baidu Inc, often called China's Google, gained 7.1 percent to $164.78.

Some say Google still has room for improvement. JPMorgan analysts said continued efforts to counter declines in ad rates might yield a major opportunity in the upcoming holiday season.

Google this year rolled out a service to help advertisers promote their products on a mix of smartphones, tablets and desktops. The move is also expected to bolster Google's overall advertising rates by mitigating the impact of mobile ads, which command lower rates.

Others say YouTube's potential remains only partly tapped. Ads on the site increased more than 75 percent in the quarter, with 40 percent of traffic now coming from mobile devices.

"We estimate that Google's key YouTube asset generated approximately $4 billion in revenue in 2012, positioning Google extremely well for the strong growth in video advertising," RBC Capital Markets analysts wrote.