Charlie, Chuck and Vicki
Create a diagram of where your new members are coming from. Then work out who are the connectors, and who influencers these connectors. You need to treat these people differently.
Charlie told Chuck about this blog. Chuck posted about this blog in his project, which sent a few hundred people here. Amongst these people is Vicki. Vicki posted about this blog to a 300 people of her followers on Twitter.
Chuck and Vicki are the uber-connectors with big followings. But Charlie influencers Chuck who influences Vicki.
Knowing these connections matters. You can offer Vicki something that will benefit her followers. You might offer Chuck the same, only with something special for ‘select’ friends like Vicki. You might ask Charlie for his advice on what would make him recommend you.