What sort of results are you seeking? I assume you mean that you want to amass followers, but I am not sure that really represents success unless they are within your target market. I hope that you don't mean to raise funding, because that can be enormously challenging for a small nonprofit to achieve in social media (compared to putting the same amount of energy and effort into other initiatives).

The first thing you need to do is define which of your target markets you seek to attract, because you need to realize that nonprofits have multiple customers. The recipient of services is one client, the individual donor is another, the institutional donor is a third, the volunteer is a fourth, etc. Each of them wants a different experience from your nonprofit; while there are synergies between them, marketing a nonprofit is fundamentally different than marketing a for-profit because the customers who provide the capital are typically different than the customers who receive the services.

In general, the best nonprofit social media channels that I have seen are those which use the social space to create a conversation, to share knowledge, to GIVE .... not to focus on raising money.

Best of luck.