You will need access to academic journals for academic research on volunteer management, including retention and recognition. I don't have such access online. The nearest university library to me that might have it is quite a schlep (about 40 minutes away), and this week, I don't have time to do such research.
Journals that will have this information include:
The Journal of Volunteer Administration, published quarterly by the Association for Volunteer Administration (AVA). This journal is no longer published (AVA is long gone), but its back issues should be available anywhere that sells or provides access to academic journals, and volunteer retention/recruitment did come up in some articles.
The Journal of Community Engagement and Higher Education It's focused on higher education, but still worth reviewing for research regarding retention/recognition
Gateways: International Journal of Community Research and Engagement
The Journal for Civic Commitment: a twice-yearly, online journal dedicated to service learning and civic engagement
For a non-USA perspective, try the Institute for Volunteering Research http://www.ivr.org.uk/
There are several books that talk about volunteer management and recognition, which are focused on practitioners rather than researchers. These are all available for purchase here: http://www.energizeinc.com Again, a university library may or may not have these. A better bet might be your nearest nonprofit support center (for instance, the one in San Francisco is called CompassPoint). I have yet to find such a center with a library here in the Portland area (I just moved here in August).
Remember that this research or even practitioner materials will rarely mention the Internet; rather, research and practitioner books are all focused on traditional volunteer management, for the most part. But that said, traditional volunteer management includes how to support a variety of demographics, and a lot of information about turning one-time event volunteers (say, a beach cleanup) into long-term supporters -- in other words, practices that are easily adaptable online.
You might want to post to the ARNOVA list and say who you are and what you are looking for. ARNOVA is made up almost entirely of academic researchers. They don't like doing other people's research for them, but they are happy to recommend articles they themselves have written.