In an ideal world, activists would need no motivation other than the desire to fight for freedom. In the real world, activists are motivated by recognition among their peers. This has another advantage. Dormant members may notice the recognition being received by the others and then feel inclined to participate themselves. Grass-roots comes from the bottom up.
Leadership comes from the top down.
If you are an officer of your party, get out and pound the pavement. Lead by example. You took the responsibility, now use it. If you aren't an officer, you still can lead by example. Your goals should be outreach and name-recognition.