Technically "whom" is the correct form but "for" is a preposition and you must not end a sentence with a preposition so the grammatically correct way to write the question would be "for whom are you looking?"
This link has a pretty good explanation. http://www.ehow.com/how_5564178_use-whom-english.html
I can explain to my friend what you say!
Good luck!
Technically "whom" is the correct form but "for" is a preposition and you must not end a sentence with a preposition so the grammatically correct way to write the question would be "for whom are you looking?"