I went to Fiverr and hire a really really REALLY cheap social media manager from Bangladesh. On my channel ("Decker Poker"), I do "Let's Play" videos of me participating in online play-money poker tournaments. Recently I won on a tournament and while it was in the pipeline awaiting my editor's attention (she another cheap hire from Fiverr), I told my social media manager to promote the H*ll out of it on its release day and even hired a few other people over at SEO Clerks to do additional SEO work and social media marketing. Those others later sent me Excel documents that listed where they promoted that video. I went from under 200 subs to now over 1,600 then dipped back down to 700s and the rebounded back to over 1,700. However....
It has turned out that the viewers just watched that video and a fourth of them watched the first video of the channel (another one where I won a tournament) and there has been very little carry-over to any of my other videos.
My average video just shows me making the money and usually the first-minute break. So it has been a mixed blessing. Yeah, I'm over 1,000 subs but my daily views for my average video is still only about 15 views.