n. An eye-catching or compelling item that makes a person stop scrolling through a list of posts, particularly when using the thumb to scroll a touchscreen device.
Logic would suggest that thumbstoppers are much easier to accomplish with big consumer brands like Oreos, McDonalds, and Wendy’s because there’s a wider audience of cookie and hamburger lovers than there are krill oil aficionados.
This is known, in Facebook land, as a "thumbstopper." And thus, the great promise of the digitial [sic] revolution is realized: The best minds of our generation are obsessed with manipulating the movement of your thumb on a smartphone touch-screen.
The idea was to come up with a big, sweeping campaign to market MegaRed, a premium alternative to fish oil pills, to users of the social network. Each ad had to be so compelling that it would get people to stop scrolling through their news feeds — what Facebook calls a thumbstopper.