You'd make videos (either by recording them with a camera or drawing and animating frames to make a cartoon) then upload them to your Youtube account, maybe with a link to your site in the description.
Or you'd upload a trailer about your forum saying why to join. That sometimes works.
As for not showing your face... well, what's your forum topic? For games and technology, you can get around that by merely showing gameplay or in app/on screen footage. Or by taking a bunch of existing footage, muting the volume then recording you talking over it.
