Google growth isn't clicking

Fears that Silicon Valley's Internet prodigy, Google, may be getting a few gray hairs were triggered Tuesday by a negative report about its ad business that sent its shares to a nine-month low.

The once high-flying stock closed Tuesday at $464.19, and has plunged almost $300 from its high of more than $740 in November, amid worries the search giant may not escape the effects of the slowing economy.

Google's paid "clicks" on search ads fell 7 percent between December and January and have not grown from the previous year, according to comScore, which measures Internet audiences. That report sent Google's shares down 4.6 percent Tuesday, and followed Monday's 4.2 percent fall.

That Google is a moneymaker is not in doubt, but investor confidence in its ability to keep that growth stoked has ebbed.