At present, social media is full of information. Some of that information can be used as source data in various tasks. Therefore, citing social media documents is more common than before.
Bradley (2008) explained...
BRADLEY, P., 2008. Word of the day is 'exaflood'. In: Phil Bradley's weblog. 29 April 2008 [viewed 9 May 2008]. Available: http://philbradley.typepad.com/phil_bradleys_weblog/.
Talikka, M 2017, Facebook update 2017-08-25. [Cited 2018-03-19]. Available: https://www.facebook.com/groups/495046854001106/
More information about citing social media documents for example in the following site:
Internet search engines return information about social media publications when a search is performed. Videos are also found e.g. via YouTube, tweets in Twitter, Facebook updates by using the Facebook search. It is important to remember source criticism and copyright issues when that kind of information is used.