You might consider starting a Welcome thread, or an Introduce Yourself thread.
Or one or two other threads which invite personal contributions, such Your Collection or Your (Funny) Stories or whatever fits the nature of the forum.
And you might consider keeping a State Of The Forum thread where you post now and again to comment on how many people have joined, which threads you’ve most enjoyed, and so on.
(Or State Of The Community, or whichever term works for your case.)