Just to piggy back on this and specifically about building an active social media presence:
This is where something like Buffer and Hootsuite really come into play. With these tools you can schedule tweets, FB posts, G+ posts (Hootsuite only) and so on to go out on any part of the day.
This means, when you have a spare hour or so on a Sunday, you can find some articles relevant to your niche, pick 5 a day, schedule them to go out at different parts of the day and set it to go. You've now got a natural looking, active social media profile.