Reddit, Twitter and Instagram. I tried out some Facebook groups but that didn't work out so well haha, didn't get that much feedback. Need to get on Google+ groups though as I've heard people have been pretty successful with that!
That is a good question. For now I share my videos on my Facebook page, Twitter and G+ with the hashtags and also on some subreddits that allows self-promotion. I also share on YTTalk and Sharee. But for LP channels is much more difficult compared to other types of channels (and if you add to that the subject of my LP's, indie/horror games, you obtain some not really heart-warming.)
I'll share it on my personal FB page, on Twitter, sometimes in relevant Google+ communities if i can find them, and usually on specific subreddits.
Of these, I'd say that Reddit is consistently/reliably my best source, Google+ is situational, I get a handful of views from my person FB page, and then Twitter is probably the least effective for me currently.