Advertising agencies constantly stress the importance of a social media presence to their clients.

Whether it be Facebook, Twitter, Instagram, or Pinterest, agencies hope their clients realize the strong potential of these important resources.

We took a look at the Twitter accounts of the top ad agencies in the world -- ranked by revenue, per Ad Age -- to see if they practice what they preach. Do they use social media effectively? Do they communicate with followers in a meaningful way?

It turns out, some agencies want their clients to do as they say, not as they do. Many agencies let weeks go by between tweets. Think about that: How can an agency recommend an "always on" social media campaign if it can't handle its own Twitter account?

We ranked agencies by total number of followers. Because large agencies have an advantage over smaller ones in terms of collecting followers, we then gave each shop a separate, subjective percentage score based on how useful and interesting their Twitter stream was.