"Teenagers know nothing and do not help society in the least bit possible." This is some peoples' opinion on teenagers, but not all teenagers are like this. A lot of teenagers do help out in society and help to make it better. Some volunteer, work, etc, etc. Not all teenagers are bad! Everyone wants a good society to live in and enjoy.
Firstly, there would not be many fast food restaurants or clothing stores available if it weren't for teenagers because a lot of the time they are the ones who work there. You don't find many people in their 40's working at stores like "garage" or "subway". Teenagers work in lots of clothing stores and fast food restaurants, which allows those stores to stay open. So, in this way, teenagers help the economy. By working at a younger age (14-18), allows teens to get good work experience, so that they can be a better worker when they are older.
Secondly, a lot of teenagers also volunteer. They volunteer at hospitals, libraries, pet stores, and lot's of other places. At the hospital, they can give a hand with simple tasks that must be done, or help make a patient smile. Some libraries have teenagers read to younger children, or teach them how to read. They may also have teens put away books, or help check them out. At pet stores, they will get teens to help feed the animals, or clean the cages. Some teens volunteer to beautify the city by washing graffiti off the walls of buildings, or even plant trees to promote the environment. Best of all, those are just some of the places they can volunteer. There are many, many more places. You just have to ask around.