(Includes additional comScore data, stock prices)

Microsoft Corp.'s (MSFT) new Bing search engine continued to gain market share in its second week of availability, said data tracker comScore Inc. (SCOR).

The software giant, long an also-ran to Google Inc. (GOOG) in the search space, is hoping Bing creates a beachhead to have Microsoft become a bigger player in the online-advertising arena. A $100 million marketing campaign is supporting Bing's launch.

Microsoft's share of search results pages, a measure of the intensity of search activity by online users, climbed to 12.1% last week from 11.3% a week earlier and 9.1% at the end of May, said comScore.

ComScore senior vice president Mike Hurt said the data "reflect a continued positive market reaction to Bing in the initial stages of its launch."

In May, Google's U.S. market share hit a record 65%, up from 64.2% in April, according to comScore. Yahoo Inc. (YHOO) remained stable at 20.2% while Microsoft (MSFT) reached a record low of 8%, down from April's 8.2%.

comScore said Microsoft also saw a rise in the amount of Internet searchers using its Internet-search service, to 16.7% last week from 15.8% a week earlier and 13.7% in the last week of May.

Shares of Microsoft and Google were fractionally higher in midday trading while Yahoo was down 1.4% at $15.73.

-By Kevin Kingsbury, Dow Jones Newswires; 201-938-2136; kevin.kingsbury@dowjones.com

(Scott Morrison contributed to this story)