Friend asked me to be a co-signer....?

A friend of mines recently asked me to co-signed for him for a 15, 000 loan....I told him I could not because I'm rebuilding my credit after a bankruptcy......and it is still low......he said his score was low too and could not get the loan.....I provided him with the 3 major credit agency and I told him if he wanted I would try to help him build his credit by finding mistakes on his credit report.....or getting deleted inaccurate information ....I called him several times and he is not answering my calls........I do value his friendship...but I can not sign as a co-signer at this point.....