How the bleep do you gain more social media followers?

I have Insta/FB/Twitter. I post content that people like (it gets a good amount of engagement, likes, etc). However, I cannot for the life of me turn it into more followers. I started using a social media agency (TagMaven.Com if anyone is familiar) and they're doing a pretty good job so far. But if I want to do it on my own to learn some more and not have to pay a monthly fee. What's the secret sauce? Is it just needing at least one thing to go viral? Is it using hashtags well?

And if you would like to start making money online, we have a special system for you. Click here to access