I have noticed a few start ups that have launched recently have used PR firms to make these announcements and to make meeting requests etc. That is fine, but the PR firms have reached out to both new contacts and existing relationships with the companies/individuals seeking attention.
My advice is PR firms should only be used to build new relationships and do more general distribution for these types of announcements. I think you will be significantly more successful in getting the attention you desire through personal emails to your existing network. You can then defer to your PR firm who may be handling scheduling etc. Just don’t undervalue the immense benefit of existing personal relationships as these are the people will likely be most supportive in you very early days of business.