how to start a convo on facebook?

[Thats Right]

With people i don't know but have mutual friends with?

[Lenny_4_ever]

Hey, aren't you also a friend of "insert mutual friend's name"? Didn't I meet you in "insert place you met"? (Scrap the last part if you haven't met in real life.)

[obscurant1st]

Goto their profile and if you see an option for "message" over there, just click on it; and there you can start the conversation by sending hi or hello.

If the option is not there, they might have disabled the feature in facebook "privacy settings" and you will not be able to make a conversation with them!