Lost my unlocked iphone 4s? It has a passcode?

Hi so i traveled to israel with my mac book and my iphone 4s its unlocked has a sim card, yesterday i lost it i don't know how, the iphone has my pictures and my personal stuff and emails, but it has a passcode, and its not an esay one, the thing is i can't track the iphone using icloud, cuz the phone has no internet, now y question is, can the theif use that iphone, can i do anything to delete all my stuff from that iphone, can that person pass the lock, or hack or do anything about it, please let me knoe anything will help!

They can do a factory reset, and have full access to the phone
report it lost/stolen and it will be put on an international blacklist, and not be able to be used as a phone, but it still can be used as an.