The growth statistics for social media are truly impressive. Facebook has grown from 100 million to 200 million users in less than eight months. Twitter's audience grew 76.8% in just one month, from February to March, and currently has seven million unique monthly visitors. And less than one month after she started Twittering in April, Oprah already has 800,000 followers. No wonder 2009 is being called the year of social media.But as Gary Tseng of Procter &amp; Gamble's Digital Marketing Innovation team reminded his audience last week at the Bazaarvoice Social Commerce Summit, social media is just one of many "boats" on the "ocean" of word of mouth.For brands, the opportunities to activate word of mouth - the most important purchase influencer for consumers - should not be limited to social media. And yet for many marketers, social media dominate their discussions about word of mouth, rather than being just one (speed) boat in a much larger and diversified fleet.One big marketing channel that is proving its ability to do an impressive job in stimulating word of mouth is advertising - yes, advertising.According to statistics generated by our firm, there are 3.3 billion brand impressions created every single day in America via word of mouth. And fully 20% of these word of mouth conversations are stimulated by advertising. That's 660 million conversations per day.As important from the perspective of the marketer is the fact that ad-influenced WOM brings with it more enthusiastic recommendations. When a word of mouth conversation includes references to advertising, it is 20% more likely than other conversations to include an active recommendation to buy or try the brand being discussed. Thus advertising not only stimulates word of mouth, it also helps to stimulate brand advocacy.To better understand the size and scope of advertising's ability to spur word of mouth, let's take an example from research we conducted on behalf of ESPN, and presented recently at the Advertising Research Foundation's Annual Convention. Throughout the most recent professional and college football season, we tracked word of mouth levels for major advertisers and sponsors of ESPN's coverage. We compared the amount of word of mouth for these brands among users of ESPN's various properties (ESPN, espn.com, ESPN: The Magazine, ESPN Radio and ESPN Mobile). We compared WOM levels for male ESPN viewers, versus males who were not viewers.The results were dramatic. To take one example (among many), for a retail apparel brand, word of mouth levels for both viewers and non-viewers were very low in the period prior to the football season. During the season itself, word of mouth levels rose dramatically, yielding more than 90 million more conversations by ESPN viewers than non-viewers throughout the season. What is more, the spike in word of mouth can be linked clearly and directly to the media plan.With estimates by some that a conversation is worth 50 cents, the value of 90 million brand conversations is significant. Even if a conversation is worth only 25 cents, there is still substantial word of mouth value provided by this advertising.This suggests clearly to us that just as marketers are focused (some might say fixated) on social media to help facilitate consumer conversation, there remains a tremendous role for advertising as well. But it can't be continuation of "advertising as usual."Increasingly, the proper role of advertising must be to drive brand engagement and word of mouth. The new challenge for creative and media agencies alike is to communicate in a way that captures the consumers' imagination, tells stories and leads to true engagement. When this happens, consumers will pick up on these narratives and themes and carry the message along via word of mouth. Not only does this help the reach to expand, but it deepens the impact dramatically, as well.Engaging brands are like engaging people -- we naturally want to invite them into our conversations and into our living rooms. Getting invited into consumer conversation should not be a goal just for the social media team, but for everyone involved in your marketing communications.Welcome Ed Keller as our newest MediaBizBlogger.Ed Keller, CEO of the Keller Fay Group, has been called "one of the most recognized names in word of mouth." The publication of Keller's book, The Influentials, has been called the "seminal moment in the development of word of mouth." Ed can be contacted at email@example.com.