Once you have accounts with followings they can support each other, RT each other's posts, get reach that way. I think that's how any in-house influencer marketing companies got started, they built Facebook like pages over the last decade then just used them to make new pages. Moviepilot did this also, apparently spending a year building the pages before they built the website! That is brilliant forward thinking. Regarding Insta/Twitter growth from zero, Austin's advice seems pretty solid?