Of the 22 sites, most did not contain any ads targeted to consumers based on their online behavior, according to the January study .

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Even if teens have not actually engaged in risky behaviors but merely brag about them online, this can still affect their future behavior, said study co-author Dr. Dimitri Christakis, professor of pediatrics at the University of Washington and director of the Center for Child Health, Behavior and Development at Seattle Children's Hospital.

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Every few weeks, it seems, I hear about a new study that reveals how online brand conversations are increasingly influencing consumer buying behavior.

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In a recent Kelton Group study my firm commissioned, titled Social Commerce: Buying Behavior and Influence Online, consumers were asked who they were likely to trust the most and least for product recommendations.

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