Yes, social networking sites show the better ways to increase traffic to your site/blog. But it doesn't work when your posts or content fails to attract them. For example if your post content irrespective of time you may not get better traffic. I'll give you a detailed explanation on this.
Let us think that Apple iPad mini 2 is going to be released within a month or two. So, if you post topics on iPad mini today, there are more chances that it attract your page followers. But if you post the same topic after 3 months i.e one month after the release of mini 2 there will be no use.
So, whatever the platform you choose, content should be unique, fresh and attractive. I personally think that Google+ and twitter are better, because Facebook is being used only for entertainment. And in G+ and Twitter you can find more tech lovers and geeks who are more interested in technology and its trends. So, that's clear now.