my SIMS don't see each other as each character is a separate game?!?

I have just returned to the game, created a new character in a world, played it, lovely job. Then created another so they can befriend each other, but the lot is empty and the character does not exist in the other one's world. So I repeated it 3 more times and each time same result. I create a character but it's almost as they are separate games not connecting... please help