I usually use my PC to browse stack exchange but I've recently downloaded the android app for more constant accessibility. However on the app when I see a comment that I appreciate and find useful there is no button to up vote it, nor is there a flag option. Am I not looking in the right place or is there no way to do this?
I don’t use the Android app, but you should be able to tap the comment and see a toolbar at the top of the screen. From there you can upvote, reply, and flag. See here for more information.
The iOS app works similarly but the menu is under the comment.