Romanized: Anata ga inai kara, watashi wa samishii Literally: Because you're not here, I am lonely
As can be seen from the above literal version, there is no way to exactly say "I miss you" in Japanese, so the above is one approximation of the meaning. However, Japanese themselves will not often say it this way. They would usually say
ã‚ãªãŸã«ä¼šã„ãŸã„
Romanized: Anata ni aitai Literally: I want to meet you (Which is what "I miss you" _really_ means, of course! ^_^)
If there's no way to meet them again (because the person is dead, for example), one could say