A good stop for resources on YPE is Act for Youth. YPE is described as:
an approach that engages young people in evaluating the programs, organizations, and systems designed to serve them. Through YPE, young people conduct research on issues and experiences that affect their lives, developing knowledge about their community that can be shared and put to use. There are different models of YPE: some are completely driven by youth, while others are conducted in partnership with adults.
A list of resources points the reader to other literature on YPE.