Twitter is censoring the #occupywallstreet posts, and is preventing the activists from trending and getting the news out there to the people that need to know. They are trying to stifle you, and prevent you from fighting the good fight.
DIASPORA and Friendica are social networking platforms that are similar to Facebook, and allow for hashtags in posts for activism. They’re both free, open source, and you can even install them on your own server if you really want to. (Here for a Friendica install guide.)
For DIASPORA, I would recommend registering on a pod such as Diasp.org; they allow for trending topics, are part of a decentralized social platform (multiple sites can communicate to one another), are against censorship, and it functions like a hybrid of Tumblr, Facebook, and Twitter, in a way that makes sense.
The platform is in heavy development, with a lot of exciting features coming. You can learn more about it here. You can find many different pods, many of which are capable of talking to one another seamlessly, right here.
“Well, that’s great and all,” you say, “But what about Twitter?” For that, there’s StatusNet. One of the most popular StatusNet installations is Identi.ca. It, too, is decentralized, albeit not perfectly yet.
When you take control of your own network presence and your data, it’s empowering. No one can or will censor you. Your privacy is truly respected, and you are not treated as a product through an “identity service”. It’s great, and if you want to keep the cause moving, you might want to switch to this as a social platform instead of Twitter, Facebook, or even Google+, which will all continue to censor you.
DIASPORA is even working on an upcoming feature where you can have an account, and if you don’t like the server you’re on, you can download your data and migrate to a different pod on a different server. Seamlessly. And you’d keep all of your friends, posts, pictures, comments, and data.