Social media is expanding the power of word of mouth marketing. But as always, WOM is hard to measure. Forrester is attempting to rectify that with their latest measure, Peer Influence Analysis.

In keeping with traditional WOMM thought, Forrester says that Mass Influencers, who make up just 16 percent of all online Americans, are responsible for 80 percent of the brand impressions in online social settings.

But the big winner is Facebook:

Of all the social influence impressions, Forrester found that 256B were on social networks, and another 1.64B were on other forms of social media (including blogs).

Forrester divides the Mass Influencers into two groups: Mass Connectors and Mass Mavens (3.7% of the online population falls into both categories). Mass Connectors have a lot of online friends—537 total across all networks, Forrester reports. Mass Mavens are people with a high level of expertise in their field. While Mass Mavens are driven to collect and share facts and opinions, Mass Connectors are driven to know others. Naturally, both frequently post about products and services.

As always, Influencers are the Holy Grail of WOMM. Unfortunately, Forrester doesn’t offer a whole lot of advice on finding those influencers. However, once you find them, Forrester says, don’t just use the same campaigns you’d use with the rest of your social media efforts, or with your “social broadcasters”:

Social Broadcasters are the “famous” individuals in your market, like Robert Scoble or Michael Arrington for consumer electronics. While they can achieve a great number of impressions, they cannot equal the power of unleashing thousands and millions of Mass Influencers. You need separate programs for Social Broadcasters and Mass Influencers.

What do you think? How do you find influencers? Are they still as influential as this study indicates?