Thunderclap - is this a good tool for authors?

The final book in the Nightingale Chronicles series.
Out July 28th .

 A writer friend of mine, Jane Holland, asked me to participate in her Thunderclap campaign. I've never heard of this but was happy to help. It's usually a tool for good causes but is occasionally used for books as well.
I thought I'd try for my next book – the second and final part of The Nightingale Chronicles – One Good Turn.
So far I've only managed to gather just over 50% of the required one hundred supporters. I'm sure I've got more friends than that so I don't know why they are so reluctant to sign up.
I then discovered from two of them that they didn't want to allow Thunderclap access to their Facebook account. I tried to explain that this was no different to allowing a friend of a friend to post on their timeline – that it was a once only permission – but I don't appear to have convinced enough people that this is the case.
I'm not sure what else to do to encourage some of my thousand friends on Facebook/ thousand twitter followers and six hundred and eighty subscribers to my e-list to take the plunge.

The first book in the Nightingale Chronicles series

On the plus side I do seem to have gained more pre-orders than I expected so perhaps people who didn't want to sign for the Thunderclap have done this instead.
I had significant success putting the first book in my "At Pemberley" series free, with sales of the other two books going from almost non-existent to pleasing.
I put "For Want of a Penny" free last week so don't know if the extra pre-orders were the result of that or because of the Thunderclap campaign.
I believe that Sir John Betjeman once said, "I'll try anything once apart from incest and horseriding."
I'm with him on the first but not the second.
I feel a bit like that about all the new promotional innovations that are now available to writers. I believe there is something called tumblr and instagram but I've no intention of trying those.
Here is the link to my Thunderclap campaign:
Click here
 Fenella J Miller