I would say maybe opening a Tumblr for it.
Tumblr is super popular, and if you had a tumbler with lots of cool PSO content, like fan art, articles or screenshots & gifs it could gather followers and create exposure. It might appeal to retro gaming people or even others who were on PSO in the early days and "don't believe they can re-visit it".....until they're told by the posts there that it's possible & how to come here and actually do it.
There's already been some projects with it people did like a chao garden or that one team doing 'updated graphics' or something.
Tumblr's also good because you can 'reblog' to gather other people's PSO content into 1 area there without it 'stealing', so you get a curated selection of stuff that promotes PSO that you both make AND find. It's free too, which really is the best. Followers can then interact with you/ask questions, and you can put links to here in whatever post you want.