San Mateo-based AdMob said this morning that the firm has raised $12.5M in a Series C extension round, from Draper Fisher Jurvetson Growth Fund and Northgate Capital. AdMob, which operates a mobile advertising marketplace, said the new funding brings the company's total Series C funding to $28.2M. The firm had earlier announced $15.7M from Sequoia Capital and Accel in the round. AdMob said it has been using its Series C funding to hire local staff in key markets and add new language interfaces, as it expands in Western Europe, India, South Africa, and Japan. The funding brings the company's total raised to around $46.80M since 2006.