Formal:
* Тебе не хватает (tebe ne khvataet): This literally means "You lack" and can be used to say someone misses something or someone.
* Ты скучаешь (ty skuchaesh): This means "You are missing" and is more direct.
Informal:
* Тебя нет (tebya net): This means "You are not here" and implies missing someone.
* Ты скучаешь? (ty skuchaesh?): This is the informal form of "Ты скучаешь" and means "Do you miss?".
* Ты по мне скучаешь? (ty po mne skuchaesh?): This means "Do you miss me?" and is a more specific way to express missing someone.
Example:
* Тебе не хватает меня (tebe ne khvataet menya): You miss me.
* Ты скучаешь по дому? (ty skuchaesh po domu?): Do you miss home?
* Ты по мне скучаешь? (ty po mne skuchaesh?): Do you miss me?
The best way to choose the right phrase depends on the situation and your relationship with the person you are talking to.