Took a loan in my name to purchase car for friend but he's not paying up now

If the car loan is in your name, then you are responsible to pay it back. It doesn't matter whether the money has been taken for your personal spending or someone else, at the end of the day the contract is between you and the lender. You cannot force your friend to sell the car as you do not have any rights on it unless you are the legal owner. If you have proof that you have purchased this car (eg a receipt from the dealer), then you've got grounds to get your money back.