Chicago—Social media advertising has surpassed search and is poised to overtake online display advertising as the No. 1 source of digital media planning and buying, according to a survey by media management company Strata Marketing.

Strata's report, based on an online poll conducted in January through March of more than 90 advertising agencies processing $50 billion in media buys, found that 69% consider social their dominant media-buying platform, up 32% over the past year and a close second to online display's 71%.

Mobile advertising also is gaining steam, according to the study, and is now seen as the No. 1 source of digital buying among 30% of the agency respondents. Apple Inc.'s iPhone has been the most-targeted device in campaigns for eight straight quarters, with 75% of respondents citing it. Devices powered by Google's Android OS were No. 2, at 57%, while Apple's iPad was No. 3, at 44%.