Most organizations think about social media when they have a need: a fundraising campaign, an online voting competition, a new product, etc. There is something they have to share with the world, and which they want the world to pay attention to now. But the world often doesn't work like that. People are busy, they're distracted, they're already engaged elsewhere. Why would they drop everything to pay attention to you? How will they even know you have something important to say? Most times, they won't.
Which is why a longer-term approach to social media is so important. Social media is not about quick wins, it's about building relationships. Relationships take time to build but, once built, give a huge amount of value in return. Just as is true in your life. The way to make new friends is not to ask them to do something for you right off the bat. Better to listen, share and find common interests first.
So when you have something important to say, or, as is likely, a call to action, for example around a fundraising goal, those you have built a relationship with already are most likely to respond.
It's not that you can't convert new people, hopefully you will. But your success rate will be higher with those you already know. If you need money for a bus fare you will probably eventually get it by asking strangers on the street, but you might need to ask 50 of them to find someone who believes you. Or you could ask a friend who will help you right away.
What's more, it's your existing community who will often push your call to action out to new people through their social networks. Which is why campaigns, with time-limited call to actions are also an important part of a social media strategy: when done right they can drive people to your accounts and expand your community.
Which gives you more people you can start building a relationship with. Which can lead to more response to your next campaign and so on in a virtuous cycle.
This is perhaps my favourite slide in the Social Media for Social Change presentation I developed at Ashoka, because it says in a single image what just took me a few hundred words to say.