I've already recommended Thunderclap to other friends. I like the system of a message "going viral" if your goal is achieved (100, 250 or 500 supporters). It works great with social causes, education and communities.
People don't quite understand it (the supporters), so you have to invite everyone personally and individually. That itself isn't so bad if you have the time.
Another thing I noticed: if someone supports your campaign with one of their accounts, they will collect the "social outreach" of that account and added to the social reach of your campaign. However, the reach is purely in numbers and doesn't reflect the true reach of the campaign (which can be as low as the number of supporters multiplied by 2 - in the situation in which 1 person besides the supporter sees the message).
It's a great tool to spread your message and to connect with influencers and people in the same industry. Do not expect to see results unless you actually engage and are active in your campaign.
Thunderclap works on a pretty simply principle: at least 100 people to get a message viral, to get a "thunder clap". Connect with each of your potential supporters individually, 1-on-1 and be ready to spend a lot of time.
Create various materials and social media distribution channels, one will not be enough. Explain to every supporter that there will be no message on their timeline unless the campaign goes live, so there is nothing to fear against "spam".
I'm running a campaign against Discrimination called Recruit and Select Wisely (https://www.thunderclap.it/projects/22087-recruit-and-select-wisely?locale=en). We're trying to spread a message of awareness among people who were discriminated during an interview for a job, who either recruited and discriminated or noticed discrimination taking place in the recruitment process. And even company owners who want to offer equal chances to Talented people who may be lacking a social skill, or a specific presence.