PIIPP stands for "pro-illegal immigration puff pieces", attempts by the MSM to pull your heartstrings in their attempt to advocate for illegal immigration, giving benefits to illegal aliens, and the like. Since most MSM articles about the topic try to do that, the term is usually restricted to articles that promote the DREAM Act.
Many of these PIIPPs are nearly identical; for a very clear example, see this side-by-side comparison of two articles from different papers using the same structure.
Many PIIPPs are probably planted by groups like the American Immigration Lawyers Association, racial power groups, or small student advocacy organizations. However, until a real reporter comes clean we'll never know where all these highly similar articles actually come from.