Is this plagiarism or something similar in a master's project?
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.