HelP: Co-Borrower Dilemma

I have a co-worker who resigned last year to transfer in a work with better compensation than us, i was the co-maker of his bank loan, after a year, he stopped paying the bank religiously which automatically gets his monthly due from my salary. He works far from us but still can be located, we can still send him messages but his like ignoring it. The bank said it is not in the point that they can file legal action since ofcourse I am paying for it. What can I do to summon the principal borrower to pay, is there any case i could file against him? He should be the one paying it not me...I would really appreciate to hear an answer.