if you have just said "turn up at my cosplay station" (not literally that) try to make your "advert" more interesting to grab people in. Say what you will be talking about, what you will do on your station etc. That should grab attention
I used to be technical side on for an internet radio station for a specific crowd, the main thing you are looking for is selling point that makes you unique, If you don't have that, you won't get any listeners.
We went from a couple of hundred infrequent listeners to a couple of thousand in a week or two due to targeted and well executed advertising, with no reasonable attempt at that, and you can forget it.
I mean no offense and by no means have any knowledge of cosplay activities, but it strikes me that cosplay is a visual "hobby", with very limited chat-show appeal and that radio would therefore be a polar opposite, I'd be more tempted to suggest a podcast, vlog or blog?