Well, actually, I may have some idea why 見つけません is inappropriate; I'm less clear why 見つかりません is significantly less so.
My question is a follow-on to this answer from @naruto to a recent question (by someone else), and the brief comment exchange we had there.
Probably best if you just go there for the details, but the summary I'll give here is that the original question asked about an example sentence さっきから携帯電話を探しているのですが, with a set of choices for how to finish the sentence: [見つかりません/見つけません][。/でした。]
In the answer in question, it was asserted that 見つかりません is the most appropriate answer, as "we don't usually say" the 見つけません-based possibilities available, and 見つかりませんでした as a follow on to the given sentence, because it "sounds like the speaker suddenly gave up in the middle of the sentence".
So far, so good.
I then proposed the Japanese textbook (especially if written by an English-speaking native as opposed to Japanese speaker) might have been aiming for the actually-less-natural 見つけません, because it preserves the same grammatical subject (which would be a false reason, as this isn't important in Japanese, but it also seems like the sort of pseudo-reasoning a non-native test-creator might come up with). The response back was that 見つけません sounds terribly wrong, and no native speaker would say this.
My question is: why? As I said, I think I suspect why, and I'm about to make some guesses as to why, but then I'm more interested at the follow-up question: why is 見つかりません okay where 見つけません is not (in this context)?
What I suspect the reason to be why, lies in the fact that I will not find it is the translation noted for 見つけません (in that answer), while 見つかりません was given as It has not been found (so far/yet). The note for 見つけません makes sense for me - it's a present or future tense, and just doesn't fit nicely with 探している, which is a currently-ongoing action. Why would anyone be searching for something if they're confident "I won't find it".
But then, the 見つかりません has exactly the same tense. Why is it "exempt"? I would expect that to mean "It will not be found", in the same way that 見つけません means "I will not find it". Is it just a "special exception", or is there a more generally applicable rule of grammar underneath this (i.e., are there other examples that can be given that reflect similar situations)?
For my part, if I were not looking at a multiple-choice answer list, I feel like I wouldn't have chosen any of those, and would have gone with まだ見つかっていません (since 見つかる is an intransitive verb, 見つかっていません should not mean "is not being found", but rather "is not (yet) in the state of having been found", in the same way that 田中さんは来ています doesn't mean "Mr. Tanaka is coming (on the way)", but instead means "Mr. Tanaka came (and as a result is here)")
Or, if I want to use 見つける instead, I might say, perhaps more awkwardly (but I hope still correctly?) 見つけてありません, for an equivalent counterpart to that 見つかっていません.
How do these answers stack up against the approved (from the set of available choices) 見つかりません answer? Better, worse? And, why is 見つかりません acceptable in place of 見つかっていません, but 見つけません is not acceptable in place of 見つけてありません?