Contributing to a participatory projects like citizen science projects is somehow about asking volunteers to use one of their available capitals. It could be material e.g. computer/mobilephone (volunteer computing, or participatory sensing), knowledge/expertise (Q&A websites e.g. stackoverflow, quora), financial (crowd funding) or human capital (cultural or creativity). However the use of the social capital of volunteers as contribution has been under-exploited, especially when we know that attracting attention and maintening sustainable contribution is one of the main issues due to the volatility and the continuous partial attention behavior of web users.
As far as I know there is only one successful attempt, the famous red ballon challenge organized by DARPA. Democratizing such social mechanism will be quite useful; For instance a user wants to participate in a given volunteering project. She subscribes to a facebook application as a volunteer ready to help. When new activities/tasks are available she is notified via the facebook app or via an email. If she can’t or doesn’t have time to complete it (or automatically by default), she can still contribute by using her social capital and spread the requests/activities to their friends’ facebook wall on her behalf. So event if the user is not interested anymore about a project due to the attention span, by giving access to her social network, she still contributes as a node of the collective effort. crowdsourcing the communication.
Incentive: virtual credit based system could be used as incentive. If the task is done by one of her friends, she will get the credits (thanks to her friend) except if her friend want to participate and subscribe to the application. The point with virtual credits is to understand how to tranform them as real incentive booster e.g. transforming them in physical goods e.g. vouchers, visiting the institut, small grant for doing research , or for social recognition (belonging to a private club e.g. top contributors, or including her name in academic papers)