I would recommend an introductory visit to the school, bring a vehicle and let them touch stuff. I would be pretty informal depending on the size of the crowd. Break it down to around a dozen kids or fewer at a time if at all possible. More than that and the crowd mentality kicks in and you won't be able to keep their attention.
I do a really abbreviated first aid CPR class for one local high school's health class. Or, if the school has a healthcare or medical careers class, talk to the teacher of that group. Another good crowd to reach is when they do the orientation for incoming freshmen in the fall. Some schools do this in the spring before, others in the fall.
I love working with teens. I raised two boys and the youngest is 18. They can be a great group as long as you don't let them get control of the situation. I've worked with kids from middle school up quite a bit and they can be a real challenge at times with all the drama, but when they get on board with something, there is no beating their enthusiasm.