To locate research papers that use citizen science data, search for any or all of the following concepts, modified by the scientific discipline for which you're seeking information:
Below are a few open source search engines to get you started. Don't forget the commercial databases (Scopus, Web of Science, etc) that may also be available through your local library. Also check out Citizen Science: Theory and Practice, an open access journal published by the Citizen Science Association.
Monitor Change, a concept developed by Sam Droege of the USGS Patuxent Wildlife Research Center, encourages citizen scientists to monitor environmental and social change using iPhones, photo-stitching, and time lapse.
Nerds for Nature used this idea to monitor how the landscape charred in the Mt. Diablo Morgan fire changed and recovered by taking pictures from fixed locations for one year after the fire.
The list below is a small representation of recent research papers that used citizen science data to reach their conclusions. To locate other papers, see search tips in the box above.
Citizen Science: how ordinary people are changing the face of discovery by 
The Purple Martin: how citizen scientists and colony landlords are saving a favorite American bird by 
Quality Assurance Handbook and Guidance Documents for Citizen Science Projects
