Well, actually I think if you say "I missed you", it can be meant that you're not missing him/her right now, right ?
But if you want to say 'I miss you' as the expression you can say:
" Chan(for both male & female) / Phome(male only)
+ Khun(formal) / Tur(Informal) "
ฉัน/ผม + คิดถึง + คุณ/เธอ
I hope this clears up your answer.
Have a nice day!