Ninakukosa - it doesn't really mean I miss you. If you said it to a Swahili speaker it wouldn't really make a good sense. Kukosa - the act of not finding what you were looking for I can't really find a sentence in Swahili that would mean "I miss you". The one I can find people use they mix it with the english word by saying "nimekumisi" (I missed you). But "nimekumisi" is not a swahili word it's just a mixture of english and swahili put together so you'll never find it in any dictionary..but you can use it to a swahili person when you're talking but don't use it when it's something like an essay you're writing.