The documentation for the report_spam resource can be found here:
http://apiwiki.twitter.com/Twitter-REST-API-Method%3A-report_spam
As the original announcement mentions, it's important to realize no
automated action will be taken as a result of a spam report being
created. So don't expect an account to be suspended immediately (or at
all). Also you can only create one spam report for a given user, so
subsequent requests will have no result.
Thanks.
--
Marcel Molina
Twitter Platform Team
http://twitter.com/noradio