One of the biggest mistake I have made is to rely on something I have no control over. Don't get me wrong; Facebook, Twitter, Instagram, Snap Chat, Pinterest, and whatever else comes along are great ways to engage your audience. You are still limited on how much engagement you can have with them. You don't own the site and they can change what they will let you do at any time.
The best strategy I have found for using these type of sites is to get them on a mailing list and take control of your audience. This way no matter if all the social media disappears tomorrow - you still have these people you can contact. Get them on your mailing list and then send them to the site you want traffic to by suggesting or reviewing the site. Just put up some kind of free offer as the pinned post they have to sign up for your list to get.
This is probably the best article I have read to to understand why you need to develop your audience.
1,000 True Fans
The only way to see if they are truly your "fan" is to see if they will sign up for your list. This is where I have fallen short in the past. I just concentrated on "numbers" and didn't make much from the effort.