Yoav Ravid asks: "Is there an assurance-contract website in work?"
i.e. a site where, if there's a locally bad equilibrium that would be better if everyone changed strategies at once, but which requires a critical mass of people in order to be worthwhile, you can all say "I'll put the effort if other people put in the effort", and then if X people agree, you all go into work the next day and demand a policy change, or a go to a political rally, or change a social norm, or whatever.
Some attempts have been made at such a system. It's not that technically hard to build. But I think it'd need a couple major "flagship" Coordinated Actions in order to rally people's attention and turn it into a more frequently used tool.
So, if a good website existed to coordinate action, do you have a well operationalized action you'd want to coordinate? ("Everyone leaves Facebook at once" doesn't work IMO, because it doesn't say where people are moving to, or otherwise replacing FB's tools with.
"Everyone on one platform switches to another platform" seems viable.
"Everyone at my office signs a letter demanding change for a particular policy" seems viable (although in cases like this, where you maybe don't want your boss to know you're planning a revolution, and I'm not sure how to best achieve common knowledge without risk)
(For further reading, see "The Costly Coordination Mechanism of Common Knowledge" and "Inadequate Equilibria")