SAN FRANCISCO — Google Inc.'s stock reached a new high yesterday, reflecting Wall Street's renewed faith in the Internet search leader as it introduces new ways for advertisers to reach its steadily expanding online audience.

The shares peaked at $560.79 before falling back to finish at $560.10, up $7.27, or 1.3 percent. The rally eclipsed Google's previous record high of $558.58 attained in mid-July, just days before the Mountain View-based company disillusioned investors with a second-quarter profit below analyst estimates.

Google, founded just nine years ago, now has a market value of almost $175 billion, more than such long-established technology bellwethers as Hewlett-Packard Co. and IBM Corp. The stock has increased by more than six-fold from its initial public offering price of $85 in August 2004.

The latest run-up in Google's stock represents a turnaround from a little over a month ago when the shares briefly dipped below $500 amid the stock market turmoil triggered by a home mortgage meltdown.

Google runs the largest advertising network in the world's hottest marketing medium, the Internet.

Despite aggressive challenges by rivals like Yahoo Inc. and Microsoft Corp., Google has been able to widen its lead in search — the activity that triggers the text-based ad links that have become a huge moneymaker.

In August, Google handled 54 percent of all U.S. search requests, up 50 percent from the same time last year, according to Nielsen/NetRatings Inc. Yahoo handles 20 percent, followed by Microsoft at 13 percent.

The formidable lead enabled Google to earn $1.9 billion on $7.5 billion in revenue during the first half of the year. The company usually makes even more money during the second half because of the ad blitz in the holiday shopping season.

Google is trying to boost its profits by rolling out options besides staid advertising links.

Last month, Google began showing video ads on its subsidiary, YouTube, the Web's most popular video channel. Earlier this week, Google dramatically increased the number of ads distributed to mobile phones and unveiled a system for displaying ads on widgets — mini-applications embedded on Web pages.

Investors are betting Google's dominance and expansion efforts will yield the robust earnings growth needed to support its rich valuation. Google's price-to-earnings multiple — a widely used yardstick for appraising publicly held companies — now stands at 37 times its estimated earnings for this year. By comparison, Microsoft's price-to-earnings multiple is around 17.

Several industry analysts already are forecasting Google shares will soon surpass $600. The stock eclipsed $500 for the first time 10 months ago.