Should i help someone who doesn't want help?

My cousin Joey is 14 and is already go down the wrong path that i went down. I tried talking to him but he denies any help that me or anyone else offers. Even though he thinks nothing bad will happen hes wrong because hes already smoking and drinking. He is even huffing gas and spray paint. Ive been trying to help but he wont take it and I'm starting to give up hope for him.