How can I use major newspapers to find several examples of juvenile delinquency or crime?
This should be a very easy task for you. Just "Google" the names of the various newspapers; you will find their websites. Visit their websites and follow their links to news reports. Just by briefly looking at the headlines, you will soon be able to tell which news stories involve the subjects you are to cover.
You can copy and paste the stories onto your word processor, just for your own use....like taking notes. Read them carefully, then make notes for yourself, dividing them into categories (like break-ins, physical assault, robbery, burglary, etc.) It will also be helpful to note things like the ages of those who are written about, and other interesting materials such as whether they were homeless, poor, needing work, rich kids seeking thrills, etc.
Very soon, and without much effort, you will be able to have plenty of material for your report. You can also just "Google" such terms as "newspaper, St. Louis", or "newspaper, Chicago", or "newspaper, San Diego", to get the names of newspapers you may not already know.
I certainly can't write the report FOR you, as this is not the purpose of this site. However, with this much guidance, you should have no trouble. Good luck!