Free Methods to Gain Followers or "Friends" on Social Media Sites.

I wanna know how do you gain active followers/ subscribers/ friends and liker on the following social media sites:

Steemit
Pinterest
Instagram
Reddit

I find Facebook easier than expected in the sense that when you add someone, they'll most likely accept your friend request. But what about the social media sites I have mentioned above, how does one gain followers on those sites?

Thanks