Someone has stolen my iPhone 4S with ios 7. Please help me

Hi everyone,

My iPhone 4S with ios 7 with a passcode was taken. I didn't back up my data on to iCloud on itunes. Will the person who has taken my iPhone be able to break in and have access to my details on my iPhone 4S that has been taken. Is there a way to erase my data. This is my first time that I''ve lost my iPhone 4S. I didn't install Find my iPhone on to my 4S, Is there another way that I could track it down?

Thank you.