Do you want a few thousand more members? Partner with an organisation that has a few thousand members.
There are millions of big organisations that should have a community, but don’t. This is because it’s not easy. These organisations (event companies, universities, magazines, newspapers, companies) don’t have the knowledge, nor the people and financial resources to start a successful community.
Offer them the benefit of your fully-managed online community. A place where their members/readers can come to chat online. You might even be able to name a fee. You might even approach organisations with a struggling community.
For them, it’s a sure bet of a functioning, active community. For you, it’s a huge boost of your status.