A VC-funded startup called WhosHere is trying to steal my social network 14 years ago
Work the PR front, in addition to all the legal work you need.
Ideas:
-Start tweeting about it & create a hashtag #WhosHereThieves
-Get in touch with the TechCrunch author who wrote about about your app. This story is a big deal
-Reddit post
-Accept donations page
-The VC probably doesn't know anything about this, but they might respond if included in all the negative PR