Mobile ad network AdMob just raised $15.7 million in its third funding round. Led by Sequoia Capital's Growth Fund and Accel Partners, the infusion brings AdMob's total investment capital to $34.3 million.

The two-year-old firm says it has tripled the number of ads across its network over the past year. In September, ads served totaled 4.5 billion across 6,000 mobile sites. Advertisers include Toshiba, Comedy Central and Cover Girl.

Sequoia's Jim Goetz called AdMob "well capitalized" with "cash flow positive results," which should help the company "aggressively capture market share" in an economy that's stifled other interactive media players, including AdBrite, Veoh and Google.

"They have some of the same qualities that we saw in Google, Yahoo, YouTube and Apple, including their exceptional team and powerful technology platform."

The company shall use its funding to expand globally, hiring local staff in Western Europe, South Africa, India and Japan. It will also expand mobile ad offerings for advertisers and publishers. (Currently, both banner and text ad campaigns are supported.)

Earlier this year, San-Mateo-based AdMob opened its first New York office. Over the summer, it also launched a global iPhone ad marketplace, promising to pass $1 million worth of advertising to developers of useful iPhone applications.