Scenario: I lost a shirt on my birthday and 6 months has gone and it is found now.
1. I have found the shirt now. The shirt has been missing ever since my birthday. ('has' is not possible here because the shirt has been found? Or is it possible? eg. I haven't seen you for so long. (you're seeing that person right now) )
1. This is fine. 2. This is a little strange. I don't recommend it. It's oddly contradictory. It was missing, but since my birthday -- until when? With the present perfect, at least you tell us that the state of being missing carried on up to the present moment. 3. This is also OK. It makes me think the shirt was found earlier in this version than in Sentence 1.