I would gladly advertise for HIVE.
But...
Here are a few things I think (being a total noob at HIVE) I would need to do so:
Advertising materials - banners with the HIVE logo and some with one line benefits of using HIVE. " Tired of being banned ?" "Miss your freedom of speech?" etc.

Make / find ONE simple way of joining that has the less amount of hurdles. FB, Twit and the rest got so huge because they made it easy to get on them. We need to do the same. This may exist already and I just don't remember - I was looking for a replacement for FB and the rest and looked at a ton of different places - so kinda forget the sign up process.

And FYI - I found HIVE due to a video on YT - so maybe do a poll and see how current members found HIVE in the first place and go for more of that. Hope this helps :)