* Μου λείπεις (Mou leipeis): This is the most common and generally appropriate translation. It literally translates to "You are missing to me" and is suitable for most situations. This is a good default option.
* Μου λείπεις πολύ (Mou leipeis poli): This means "I miss you very much" and adds emphasis.
* Σ' αγαπώ και μου λείπεις (S' agapo kai mou leipeis): This translates to "I love you and I miss you." Use this only if you're comfortable expressing romantic love.
So, Μου λείπεις (Mou leipeis) is the safest and most versatile option.