If you can get in touch with this guy that would get you close. how about emailing this userid at yahoo[.com,.co.in], hotmail, aol etc and see if you hit jackpot ? Or you could reply to one of his friends and just if you can in touch with this other guy via another channel ?

All this is assuming that the other guy cannot get into this "common" gmail account and you are not enjoying looking at all the other emails that you get.