Spending on paid search ads by U.S. retailers increased 12% in the second quarter of 2011 compared with the first quarter of 2010, according to a new report from IgnitionOne, formerly SearchIgnite. By comparison, paid search spending increased 24% in the first quarter compared with the same period in 2010, according to the last report from the digital marketing company.

Overall, the quarter began strong for search advertising, the report says, but spending dipped sharply in June, with little growth compared with the same time a year ago. “While this decline did not have a significant impact on the quarter overall, it could be an indicator of future months’ performance, and expectations for Q3 are cautiously optimistic,” the report says.

The study found that Microsoft Corp.’s Bing search engine accounted for about 19% of U.S. search advertising in the second quarter, with Google Inc. taking the rest. Bing accounted for about 20% in the first quarter and 17.4% in fourth quarter of 2010, IgnitionOne says.  Spending for Facebook advertising, meanwhile, increased 22% year over year.

IgnitionOne did not release actual spending figures.