this is the link to the California version and how it works ......
California Megan's Law - California Department of Justice - Office of the Attorney General
after opening the page scroll down to the continue button , when you get to the search page type in the "zip code" (post code) 94546 and it should bring up the locations of the sex offenders in my area.
Never heard of any vigilantism in my area , though I don't think offenders are allowed to reside in the area where the crimes were committed .