How to search for a group of people in Stack Overflow? For example, I need to know posted Android questions and are from in India?
How can I find these users?
You could, at the very least, go through every [android] question and check each user's (publicly accessible) location from their profile page.
The SO API could provide some way to do this, and you might ask at Stack Apps.
Once you get the user list, what do you plan to do with it? If you want to contact each user to spam them, that's definitely Not Okay. But if you're collecting data for some larger purpose, perhaps educational, that's one of the intended uses of the data. But more importantly, if we know your goal, there might be a better way to achieve it.