In the past we've engaged with PointBlank. The contact there is Aaron Wessels.
They're a small firm which is ideal for a startup in it's early stages.
aaron wessels | principal | point-bl_nk communications
Currently we use SpeakerBox, which is good when you're volume starts to grow and you need to increase your reach. They have a good grasp into the social media scene.
You can talk to Stephanie or John.
Stephanie Stadler Wonderlick [email@example.com
John Terrill [firstname.lastname@example.org]
Hope this helps