The nonprofit world is changing drastically, and more and more donors are directing their giving based on transparency and effectiveness. To that end if you want to attract (and more importantly KEEP) new donors, you need to be open about what you're doing, measure your outcomes and define your theory of change and how those outcomes create the impact you want.
Size isn't necessarily important, but generally a proper program of impact assessment requires some upfront investment, and it's hard to sustain for organizations below a certain size. The payback is two-fold though: you know which of your programs are effective, and you demonstrate to your donors that their contributions are going to their best use, encouraging them to keep funding you. There's no silver bullet-- the social sector is more competitive than ever (over 1 million 990 filings a year), and it's very hard to be found. If you are confident in your programs' efficacy, make the investment to pitch a foundation for which the geographic and mission goals overlap. It's more work, but a foundation that believes in the mission will usually make a significant commitment to underwrite the cause because they would rather the organization be delivering change rather than fundraising.