I found a firm, New Media Strategies, that focuses mainly on twitter and other social network sites as their platform to sell communications. They specialize in entertainment, beauty, sports, retail, travel, public affairs, and more. They have executed 2,000 campaigns and have represented 85 industries. They do market research, analytics, strategy and other types of marketing for their clients. When looking through their staff, it appears that everyone is relatively young, and work from across the country. I think this is a new, innovative firm that would be interesting to take a deeper look into.