On Facebook and on Twitter, I maintain two accounts:
one I use for real stuff, and one I use for internet promotions like the following.

Marriott Rewards Plus Points
Earn points by promoting Marriott Rewards on social media.

A Flyertalk forum on this topic started up yesterday here. Marriott's website says this program is in beta, but most participants on the forum have reported no problems.

I saw nothing in the Terms & Conditions that limits this promo to US residents.