so many people try what ure trying bro... ¨my friend´s account¨ ¨my girlfriends account¨ ¨my brothers account¨ ¨the popes account¨
even many of us, at some point or another, have tried it.
your parents always teach u to ¨ask for something nicely and you will get it¨, bullshit, thats not the way of the World Wide Web. in this world, u have to read ure ass off until something leads to something else which leads to something else until EUREKA!
its a pain in the ass to go through all that, but man it feels good at the end when you get what u wanted, which rarely happens, but still at the end of the day, you will know things no one knows.
with that said, there is no way, for someone who is asking this question, to get an IP from a message withing facebook. i say IP because i imagine you want to pin point the attackers location and send a swat team to his/her place.
however, if you search a bit in google, i promise u will find usefull things that might help u out.
good luck! :P