Because of the annoyances we're currently facing with Hopsy and Pip's events on Facebook, I'd like to suggest a few ideas.
At first, it's really annoying to post what you want to donate in one single post then wait until someone manually takes the donation in your account and rewards you with the prize.
What will happen if the community of players is wider than a few hundreds people? I can't imagine the number of useless spams and the mess in one single thread...
Isn't it better to code it inside the game so for every seasonal event, it's possible to build a small building (that we can remove or store) and click on it to see the list of required items we have to give in order to get the prize? Once we have the required items in the inventory, we can click on the building and choose to donate it and get the reward immediately.