[@Juno] Hello, friend, and welcome! Sometimes RPing doesn't work out, but good on you for giving it another go! Hopefully if someone harasses you via PMs on this site, a moderator will intervene and help you out, and you won't be put in that uncomfortable situation (sorry to hear of it). 

There are many RPs based around some of the genres you mentioned, and they have appropriate tags which you might find useful. You can look in the "Free", "Casual", and "Advanced" subforums, which are categorized based on the amount of effort / ease you put into writing your posts. A lot of people are interested in Firefly, Doctor Who, and I think I've seen a few Buffy RPs as well. If you don't find anything that quite tickles your fancy, you might even try your hand in making your own RP. 

I hope that helps. Feel to PM me for any questions :)