Hopkin Explained at mike.whybark.com:

As I noted here previously, sometime around September of 2003 some fliers appeared in Seattle, proclaiming the loss of what appeared to be a small boy’s frog. “Who took my frog?” the author asked, plaintively. Concluding with a determined “P.S. I’ll find my frog,” the fliers were noted and remarked upon by at least a couple of Seattle-based bloggers, Jeff Sharman and Samantha, whose last name I do not know at present.

As Jeff notes, sometime in September 2004 the flier was introduced to an online image sharing community, where it quickly became the subject of a still-growing set of visual riffs. An enterprising individual soon registered the domain lostfrog.org, where new contributions continue to be posted.

The story isn’t quite what anyone expected. Read only if you really want to know more about the story.