Social Media
Chicago Manual 14.205-206, 209, 214; 15.52-53
See examples below for:
Notes-Bibliography Style
       1st Footnote or Endnote
           13. Comment on Sarah Palin's Facebook page, April 1, 2011, 3:21 p.m.,
       https://www.facebook.com/sarahpalin.  
       Bibliography
       Usually not cited in bibliography.
Author-Date Style
       1st Parenthetical Note
       (Comment on Sarah Palin's Facebook page 2011)  
       Reference List
       Comment on Sarah Palin's Facebook page. 2011. Facebook, April 1, 2011.
           https://www.facebook.com/sarahpalin.
Notes-Bibliography Style
       1st Footnote or Endnote
           12. Obama for America (@OFA). Twitter, September 4, 2011, 6:53 a.m.,
       https://www.twitter.com/barackobama.          
       Bibliography
       Usually not cited in bibliography.
Author-Date Style
       1st Parenthetical Note
       (Obama for America 2011)
       Reference List
       Obama for America (@OFA). 2011. Twitter, September 4, 2011, 6:53 a.m.
           https://www.twitter.com/barackobama. 
Notes-Bibliography Style
       1st Footnote or Endnote
           16. National Geographic (@natgeo), “Photo of Bering Sea by Corey Arnold,” 
       Instagram photo, April 2, 2017, http://www.instagram.com/p/BSaisVuDk7S/?taken
       -by+natgeo.   
       Bibliography
       Usually not cited in bibliography.
Author-Date Style
       1st Parenthetical Note
       (National Geographic 2017)  
       Reference List
       National Geographic (@natgeo). 2017. “Photo of Bering Sea by Corey Arnold.” 
           Instagram photo, April 2, 2017. http://www.instagram.com/p/BSaisVuDk7S
           /?taken-by+natgeo)  
Text
Notes-Bibliography Style
       1st Footnote or Endnote
           3. Joseph Black, text message to author, April 23, 2012.
       Bibliography
       Usually not cited in bibliography.
Author-Date Style
       1st Parenthetical Note
       (Joseph Black, text message to author, April 23, 2012)
       Reference List
       Usually not cited in reference list.