There is an answered question at Where is the option to add online accounts listed? It certainly isn't under settings in my system! but I don't think the answer is correct. When Elementary Freya was finally released, many tech sites published "what's news" topics on Freya, which mentioned Online Account. So how can I get Online Account working? Thanks.
1As the original question was answered by Daniel, one of the founders of elementary, the question is indeed correct.– bigbangJan 21, 2016 at 5:48
This isn't a feature that got into Freya. However looking at a couple of bugreports that target loki(the next version) it seems that it will be available in the next version.
It was mentioned here. Freya has included Online Account: itsfoss.com/elementary-os-freya-review-features Jan 21, 2016 at 13:29
That will be because the reviewers were allready testing with a beta version to be able to release the article on the day of launch. In the beta version this feature was available but it was stripped out for the stable version because it wasn't finished yet.– joostJan 21, 2016 at 17:25