Google Inc.'s earnings growth bogged down more than investors anticipated during the second quarter, raising worries that the ailing U.S. economy is starting to touch the Internet search leader.

Although Google's management maintains the company will thrive even if the economy deteriorates further, the results released Thursday caused Google shares to plunge by about 8 percent.

The company said it earned $1.25 billion, or $3.92 per share, during the three months ended in June. That represented a 35 percent increase from net income of $925 million, or $2.93 per share, at the same time last year.

Investors expressed their dismay as Google shares plummeted $42.44, or 8 percent, in Thursday's extended trading after closing at $533.44, down $2.16.

Google's second-quarter revenue fared slightly better than earnings, rising 39 percent to $5.37 billion from $3.87 billion at the same time last year.

After subtracting commissions paid to its ad partners, Google's revenue totaled $3.9 billion -- about $30 million above the average analyst estimate.

A big part of Google's earnings letdown had nothing to do with its main business of selling online advertising.

After paying $3.2 billion to buy ad service DoubleClick in March, Google had less cash in the bank and was receiving less income on its remaining money because of lower interest rates.

Those factors produced just $58 million in interest payments and other income in the second quarter, down from $137 million a year ago.