Don’t try to identify your community’s top participators before you launch.
Activity on one community has little relevance on another. Top participators in similar communities might contribute very little to your community. They might even be saboteurs.
It’s almost impossible to distinguish between paricipators and lurkers before you launch. So don’t try. You risk ignoring your key members. You might waste your efforts catering to pre-selected members you hoped would participate at the expense of those who do.
In my experience, top participators are often people new to online communities entirely. These normal people have a genuine motivation to see the community work. These are also the people who would benefit most from your help.