Blakk01,
I have had success just emailing bloggers. Unless I'm contacting someone that I have a casual business relationship with, an email typically does the trick. If you know for a fact they are very active on a particular social network, you could also try that avenue. In general you just want to use whatever channel they appear to be most accessible in. For instance some bloggers may not respond to email a lot whereas they are extremely responsive on a social network.
Hope that helps,
Shawn