If you're irritated by homeopaths making misleading claims on Twitter, Facebook or on their websites (or in-shop leaflets or any other marketing) you can complain about those claims to the Advertising Standards Authority (the ASA).
1. Make a complaint in the UK
This is the page on the ASA's website where you can make a complaint (you give your name and address but it isn't published): http://www.asa.org.uk/Consumers/How-to-complain.aspx
2. Make a complaint in other countries too
The ASA deals with claims made on UK websites or leaflets but, thanks to its cross-border agreements, it will liaise with the relevant advertising standards authority in the following countries too -
Australia, Austria, Belgium, Brazil, Bulgaria, Canada, Chile, Czech Republic, Finland, France, Germany, Greece, Hungary, India, Ireland, Italy, Lithuania, Luxembourg, The Netherlands, New Zealand, Poland, Portugal, Romania, Slovakia, Slovenia, South Africa, Spain, Sweden, Switzerland, Turkey and of course the United Kingdom.
And that's it.
There's some extra background information at: Stuff that occurs to me: What is a misleading homeopathy claim, and how to report it to the ASA
