The company's search traffic on mobiles surpassed desktop traffic worldwide for the first time in the latest quarter.
Alphabet's shares were up nearly 10 percent at $746.95 in premarket trading, far above the $713.33 record high set by Google - the company's former name - in regular trading in July.
A 10 percent rise equates to about $46 billion in market value. This would give Alphabet a market cap of about $519 billion, cementing its position as the second-most valuable stock after Apple Inc (AAPL.O), worth about $660 billion.
Shares of Amazon.com Inc (AMZN.O) and Microsoft Corp (MSFT.O), which also posted better-than-expected quarterly results on Thursday, also jumped in premarket trading, pushing up U.S. stock index futures.
At least 14 brokerages raised price targets on Alphabet's stock on Friday. J.P. Morgan and Jefferies were the most bullish, both raising their targets to $900.
"We think it's not long before mobile clicks surpass desktop, which we expect will provide a nice tailwind to cost-per-clicks, magnified by a tighter gap between mobile and desktop ad pricing," J.P. Morgan analyst Doug Anmuth said.
Alphabet said the number of paid clicks, which require advertisers to pay only if a user clicks on the ad, rose 23 percent, compared with 18 percent in the previous quarter.
With rivals such as Facebook Inc (FB.O) nipping at its heels, Alphabet had been trying to pump up advertising revenue from its mobile and video businesses, which have been much less profitable than its desktop business.
In a sign the company was becoming more sensitive to shareholders, Alphabet also announced on Thursday a $5.1 billion share buyback, its first ever.
Alphabet's new transparent reporting structure, to come into effect in the current quarter, also shows the company is becoming more shareholder-friendly, analysts said.
"The market has wanted four things from GOOGL – consistent revenue growth, margin stabilization, greater disclosure and cash back. What the market wants, the market gets," said RBC Capital Markets analyst Mark Mahaney. — Reuters
