I could give you 3 better leads than this place for online collaboration.
1. SoundCloud. Upload your own instrumental music and say "looking for vocalist" in the title. Or see who likes your tracks and message them for leads. I've been on there a couple of years and I've collaborated with about 2 dozen folks of different genres.
2. Ohm Studio. You set up a profile specifying genre and instruments played and what you're looking for and folks can message each other and get on each other's projects through the site. They even have a built in radio station that can feature your finished work. Only drawback is you have to log on with your digital recording interface plugged in or the recording software won't show up. It's free for the first ten projects (songs) then a cheap yearly fee after that.
3. Facebook groups. This is where everyone is heading these days. Once you find a group that fits, you can ignore the rest of that dumb site.