I always think of PR for a startup as really meaning "purposeful relationships". Axel's example illustrates that. Although you may be starting off with a brand you are trying to build equity in, the initial stages of a new business are more about market acceptance than anything else, at last IMHO.
That being said, even these initial efforts should be consistent with the brand framework the marketing team created...which hopefully is built on top of real research.... using screened target market users/participants... whose profile has been created...based on their needs/desires...showing sufficient appeal and purchase intent....that supports the notion a profitable business can be created.