How to start a casual conversation with a guy on Facebook?

so i like this guy and i got the guts to F/R him on facebook, i don't know if i should talk to him or not... would that be weird? and if i should what should i say? he goes to a different school than me, and the only way i know him is because i met him at this dance I went to with my friend.. he just broke up with his girlfriend as well... thanks! :) oh and i'm not allowed to date him, so yea! so should i talk to him (what should i say?)? or should i just leave it at we never talk!?