Google ad viewership up 3 pct on comsCore: sources

SAN FRANCISCO (Reuters) - Google Inc showed modest growth during February in a closely watched report released on Wednesday on how Google gets paid by advertisers, sending the company's shares down 2.9 percent.

Web measurement firm comScore Inc issued a monthly report on "paid clicks" -- a key measure of how Web searchers are converted into ad viewers -- that showed Google's paid click rate grew 3.1 percent year-to-year in February, sources said.

ComScore declined to comment on the report, saying it publishes the data for use by clients, which include companies in the advertising industry and Wall Street brokerages, which use the statistics to gauge Google's quarterly revenue trends.

Flat year-over-year growth by Google on the same basis in comScore's January report, which was released in late February, led to an 8 percent one-day drop in Google's stock the day afterward and a fierce Wall Street debate on whether Google's growth is slowing or whether other factors are in play.

(Reporting by Eric Auchard)