We will offer a totally branded platform that these firms can build/manage multiple client ecommerce sites. There's really on one in our space that does this or does it well.
Being the owner of a web design firm myself, if you want to target design and development firms, the forums on Wordpress.Org and Drupal.org is a prime place to start marketing. You could simply get involved in their forums and put your signature to the white label platform in your signature.
For social media: Twitter, LinkedIn, and Google Plus are your best bets.
Bruce
