There are three ways to cite social media content in APA Style:
If you discuss a social media site in general, without paraphrasing or quoting specific information, then all you need to do is give the URL in the text the first time it is mentioned. No reference list entry is needed.
News agencies like CNN provide breaking news coverage to millions of people every day on their website (http://www.cnn.com) and Twitter account (http://twitter.com/CNN),
If you paraphrase or quote specific information from social media but your reader will be unable to access the content (e.g. because of friends-only privacy settings or because the exchange occurred in a private message), then cite the content as a personal communication. No reference list entry is needed.
Marisa King (personal communication, March 17, 2017) stated that she found her career as a librarian both intellectually simulating and personally fulfilling.
If you paraphrase or quote specific, retrievable information from social media, provide an in-text citation (with the author and date) and a reference list entry (with the author, date, title and source URL).
Detailed information on how to format each of these elements is provided on the APA Style Blog, which includes some great examples of in-text citations and reference list entries.