1.Setup simple keylogger.
2.Crypt it with fud crypter (both run-time and scan-time).
3.Add the victim on yahoo/msn messenger.
4.Bind the keylogger stub with some image (supposedly if victim is girl, you bind the stub with boy picture)
5.Social engineer the victim and send the binded image to victim.
Now wait till victim login to facebook.
Or you can use cookie sniffer also, then its instant.