Although I'm personally not a prolific Twitter or Facebook contributor, I check both sites on a pretty regular basis to learn what friends and those I follow are up to. It's fascinating to recognise two very different styles amongst those who are prodigious in their content generation. Some are overwhelmingly positive and light-hearted in their posts while others consistently dwell on the negative. I suppose this online behaviour simply reflects real life. I'm sure you know those who seem to radiate light wherever they go, and others who cast a sense of grey glumness over everything in sight.
Social media makes it relatively easy to avoid the posts of gloom-mongers, if you choose. Not so simple in the real world, however, particularly if they're people with whom you need to have regular contact for one reason or another. Although emotions are contagious (if you're not careful, someone else's misery can get through to you too) it seems to help if you're determined to see another's burden as something you can help with, rather than needing to take its full weight on your own shoulders. Just as they seemingly can't deal with it on their own, neither will you. Share the load, by all means, but don't try to carry it for them.