Where can I find people that need baby sitting?
Write up or print up a stack of Notes with your first name and phone # Not your address in case some weirdo gets ahold of it, and go door to door, or place them on doors, Mailboxes, Ask your school office if they have any job boards. Or put it in a free neighborhood newsletter. Go to interviews with a friend or parent on first meeting and always keep in touch with your parents when babysitting for safety.
I'd suggest putting up flyers near a park or any other place crawling with children =)