Some people believe if they get the influencer, CEO, MD, star player, or expert participating in their community, everyone else will join too.
They might be right, but that doesn't change one simple problem.
Those key people won't join your community. They won't give up their time to help you. You can promise them the world, but they still won't participate for long.
If you want the key people to participate in your community, you need to build the community first. You need to bring something to the table. You need to have a highly active community that provides the influencer with even greater influence.
Once you realize this, everything becomes much easier.
The tactics for engaging influencers is simple. Offer them a regular expert column, interview them, mention them in news posts, let them know the community is talking about them, give an award on behalf of the community to them, and otherwise make them feel special.
The tactics, however, aren't the problem. The problem is building a community which attracts them in the first place.