Promoted Accounts, which will be launched "very shortly," will allow companies to be be featured more prominently in Twitter's recently launched Who to Follow feature. Like the two other products in the Promoted suite, Promoted Tweets and Promoted Trends, participating brands will be clearly designated as advertisers.
The feature should help businesses attract more followers likely to be interested in their products and services, and thus gain greater visibility. Of course, there's no controlling whether or not a new follower is a frequent user of the service, or has many followers; in many cases participating advertisers could just be boosting their follower counts without gaining any substantial increase in influence.
Costolo was enthusiastic about Twitter's success with its Promoted products so far, noting that engagement rates -- determined through a combination of clicks, replies and retweets -- are around 5% on average. The startup is currently working with a little more than forty advertisers on Promoted Tweets and Promoted Trends, and expects that that number will increase to the "low hundreds" by the end of the year.