“Traffic from Android devices has increased dramatically over the last year,” according to a report issued Friday morning by AdMob, the world’s largest purveyor of mobile ads.

In November alone, Android devices accounted for 27% of the hits on AdMob’s U.S. ad network, up from 20% in October — a 35% increase in one month.

Of course, AdMob is counting ad requests, not handset sales, so its numbers cannot be used to measure market share in the traditional sense. But its reports do provide a monthly snapshot of where the rapidly expanding smartphone market is headed. The growth in Android traffic — fueled by the release of new Android-powered devices — is one of the featured themes of AdMob’s November report.

Among its Android-related findings:

• Six months ago a single Android device, the HTC Dream (G1), generated 92% of Android traffic, while in November 2009 the G1 accounted for only 37% of requests.
• The Motorola Droid, HTC Magic and HTC Hero generated 22%, 21% and 9% of Android requests worldwide in November 2009, respectively.
• In November, 88% of Android traffic in the AdMob network was generated in the U.S. The U.K. was with second largest market with 4% of requests.
• In the U.S., the Motorola (MOT) Droid quickly became the No. 2 Android handset, thanks in part to heavy marketing by Verizon (VZ). In the U.K., the HTC Dream, HTC Magic, and HTC Hero make up 92% of Android requests.

AdMob was acquired by Google (GOOG) in November for $750 million shortly after Apple (AAPL) had reportedly expressed interest in buying its network. You can download its November report as a pdf from metrics.admob.com.

See also:

• Where in the world are Apple’s 78 million handsets?
• The smartphone wars, one year later

[Follow Philip Elmer-DeWitt on Twitter @philiped]