Facebook lemming 

Noun:
One who participates in the daily viral spread of a Facebook survey, app, game, chain letter, or similar device but does not actually initiate the spread of it nor is creative enough to do so. A Facebook lemming only mimics the activities of other Facebook users.

Origin:
Macrodot circa 02/02/2010

"Im tired of getting Farmville updates from Susan. She is such a Facebook lemming!"

Facebook lemming by macrodot February 3, 2010