Japanese people don't say I miss you directly.

They often use ”会いたいです” to express their feeling of missing someone.

**会いたいです=I want to meet you.

Well, you could say, あなたがいなくて寂しいですよ (anata ga inakute sabishii desu yo (you may remove the "desu" if you're not obliged to be polite)). A more lliteral translation of that would be something like "I am sad from loneliness because of you not being here."
not a native :)

Nacir,

It depends?

I mean a boy

Or a boy?

Hmm, so you are missing a japanese girl :)