Practically, focusing on the things you can change (mostly small scale evils in your community) will have the highest degree of positive effect, rather than focusing on stuff you are bombarded with online that is out of your control (mostly large scale evils).

However, don't think you get vindicated from duty just because the task is impossible. You are as just as much responsible for yourself, your family, your friends, your community, as you are responsible for the person living on the other side of the globe. Whatever you decide to do with that information is up to you, but you will suffer with any of those who suffer, whether that be in life or death. Only the delusional think they can escape righteous judgment.