Sentences I translated:
Have you found the key you lost yesterday? - Yes, I have. - Where have you found it? - It has been in my pocket.
The key says:
Have you found, lost; yes, I have; did you find; had been.
My point of view:
We are talking about current status, we don't know whether someone we are talking to has found the key, so Present Perfect (have you found) goes well here. This action was performed at a stated time - yesterday (lost), agree. The result or may be personal experience (yes, I have).
Going further, why Past Simple? We know he has find it, past completed action, it no longer interests her/him? If so, Past Perfect is acceptable and fits well, since this experice took place before the fact of its finding.
I know there were to many topics connected with this thematics but still.