AOL's Platform-A remains the top ad network in the US, reaching nearly 176.5 million US internet users, or 91.5% of the total audience, based on April ad-network rankings released by comScore, Inc, reports MarketingCharts.

Platform-A is followed by the Yahoo Network, which reaches 167.1 million Americans online. Google Ad Network, which reaches 164.5 million US internet users, ranks at #3.

New ad network FOX Audience Network ranked #6, reaching 149.2 million people, while several ad networks in the top 25 achieved double-digit growth in the past year. These were led by by Turn Inc. (up 121%), CPX Interactive (up 88%) and 24/7 Real Media (up 48%).

"Each of the top 25 ad networks has expanded its reach during the past year," said Jack Flanagan, comScore EVP. "It almost seems that new ad networks are emerging every day, each aimed at helping advertisers achieve their campaign objectives, whether it’s to deliver reach and frequency or to target a specific audience segment."

comScore also released its Ad Focus rankings for April as part of its roundup of top websites for the month.