Demi Lovato became famous when she became a Disney Star way back in 2007. She started working with the Disney Channel and because of that, she landed a short part on the television show called "As The Bell Rings". The role she was playing ended but she was then discovered. She was then cast as Mitchie Torres in "Camp Rock" and was given the starring role.
As many others before her, her beginnings were humble indeed but she went on to accomplish great things and to become famous. You've got to start somewhere and she certainly did that and has a great fan following now, years later.