I've never had much luck with the "share this with a friend and get ___" campaigns. It probably seemed too gimmicky.
I doubt crypto types would find it appealing, we've all been barraged with ads for so many years, most of us have become immune to them.
ie: When was the last time you actually stopped for a second and looked at a 468x60 banner? I think we've trained our brains to ignore that stuff at this point.