Is this plagiarism or something similar in a master's project? I am a master's student in 3rd world Asian country. My master's thesis guide (who was from a different institute) abandoned me after giving a research paper to read. Now, with no guidance left as no-one in my institute works in analytic number theory, I began reading the papers related to the first paper. I read 5 papers in total and in my thesis I will write in detail about the details which were not covered in the papers (like detailed steps and proofs).

But, as I had no help I posted questions on mathstackexchange and some which were not answered on MSE were subsequently posted on Mathoverflow. I am really thankful to the community because without their help it wouldn't be possible to completely understand the papers. One professor in combinatorial number theory (who recommended me to another professor) agreed that I could write his name as a supervisor (my institute has rules that he had to be made a co-guide earlier even when I didn't know my  guide will not work with me). 

I don't want to write in my master's thesis that I took help from Mathstackexchange and Mathoverflow because it could create an impression that I don't know enough mathematics. But if I don't acknowledge it, is this plagiarism? It doesn't seem right that I write the names of all the users as I have asked about 10-12 questions there. I think writing all those names will create a bad impression of me. The evaluators in my university may not understand the situation. I have worked really hard on thesis despite the trauma of my guide not replying to any of my email.

Can anyone please tell me whether I am plagiarising?
Passing off others' work as your own is plagiarism, acknowledge the help you were given, there's no shame, on the contrary, you'll be praised for initiative.  

You needn't necessarily* provide references to individual posts or your account, which will avoid privacy issues.

You can provide the names of those that helped. If that poses a privacy concern (e.g., you can be identified, because the group that helped you didn't help any other individual), then you could omit some names (e.g., names with lower reputation) and mention that you've done so for anonymity. 

You could offer to privately reveal direct references to your examiners, as long as those references are kept confidential.

* Case-by-case decisions should be made on whether an individual post merits referencing directly.