I would say YouTube and perhaps Quora (if that counts.) Really, though, forums have worked best for me but that is a slow way to grow a following if you do it right.
You have to find forums related to your own expertise and start out by just getting to know people and contributing info. Over time when people get to know you and you become part of their communities, you may be able to lightly advertise or people may just ask what you do.
Doing that has brought me about a third of my early business, but I mostly stopped due to time. It generally works best on discussion forums that are not about selling things (like writing, art, etc.) instead of forums like this one where people all want to sell something.