How do I count the number of Facebook likes in articles?
Probably setting the layout to button_count will do all the magic ;) 
This should be available in settings, or can be changed in MYTHEME_preprocess_fblikebutton.

Or use modules which provide this functionality, like:


social_counters and shariff have D8 versions.
views_fb_like counts your likes. (D7 only yet)
facebookshare implements this in combination with social_stats. (D7 only yet)