Now I don't know all the details so let's do this in two parts. Those parts will be the most likely scenarios, This is your stepson and a boy in your neighborhood.

Stepson

If the boy is your stepson then your role isn’t the disciplinarian. This isn’t really gonna work for two reasons the teenager doesn’t have that type of bond with you. The other reason is that the biological parent will eventually take offense to you disciplining their child. They may be ok with it at first but they will eventually take the child's side. So thinking you are going to be the lord of your manor is out the window.

Your role is to be a mentor. In fact, this role really needs to be what all parents are for their teenagers. They're at the point now that have a mind and they have free will and trying to herd them like they are 8 simply makes the rebellion in then go harder the other way.

To mentor the teen, include them in your life. Talk to them but don't lecture. Seek first to understand what they are saying before you ever try to be understood. The understood part will come but if you just do the hardest thing possible and just listen they will actually turn to your for advice before they turn to the moron friends.

The kid in the Neighborhood

For the kid in the neighborhood if you are wanting to help a young adult out you may want to involve their mother in the discussion because if you don't have her on board you will be fighting an uphill battle because the mom may feel that you are trying to take her child away. When in all reality you are just trying to inject some strong masculine influence into his life.

When she is on board then you again include the kid in your life. invite them to go camping. If you are going on a hike then share your time as freely as you can. Again like the stepchild you are a mentor. You don't have the power to discipline. So you have to talk to them and listen to what they are saying. Understand what is coming out of their mouth and let them ask for advice.