The internet started as computers that were connected and could communicate data, but what it effectively did is bring the people closer together who were sitting behind the computers. The data became stories and conversations. The 'old' web, with pages to read but not much ways to interact was called the web 1.0. But now a lot of social sites are available where people can meet virtually, dicuss, become friends or achieve something together.
Using social media is important in any communication strategy. Why? Because sometimes a news item can go viral. We people don't really trust computers, but we do trust what our friends are saying. If they recommend something to read or look at, or if we think they are looking at something interesting, we will be triggered to find out what it is.
People are invited to become members of legions of websites nowadays. But we are also very wary of it. First of all, for each site we have to remember our login credentials, but secondly: how safe is personal information at each site? Better to use a website we're already member of and that everybody seems to trust, else they wouldn't be members, right?
Having a website is important, but primarily perhaps to give information and to allow people to find you via Google and other search machines. If you really want to interact with people, then having a page or group at facebook, LinkedIn or elsewhere might be more efficient than hosting a forum on your own site. People will engage with your cause faster if you go to the sites they're already member of, instead of trying to lure them to your own site.
Don't underestimate how hard it is to build up a community. It takes time for people to build up trust in you and your community. You will have to invest a lot of time and effort into gaining that trust. Also, most people are primarily followers and not so much creators themselves. An interesting website (in Dutch) with a lot of information on Social Media theory and therefore on how to best implement Social Media:SocialMediaModellen.nl
Social Media are powerful in spreading the word, but only if people actively share what you do. If people hit a 'like' button, or share something, it becomes visible to all their friends and connections. If a few of those like it in turn, the virus keeps spreading: your message went viral.
On the other hand, if you use facebook as a medium, the most people you will reach will be your friends and family. But are they also your target group? And do they share and like what you say? Try to find groups of people who will be interested in your message and make your messages interesting and relevant for them.