My exgirlfriend who now works at my place of employment is slandering me online?

my ex girl got a job at my workplace but later we broke up and it got ugly. Now she is slandering me on the internet on sites like www.dontdatehimgirl.com and www.dontdatethisperson.com. Should I take this up to HR and call a lawyer? Any information would be helpful. Thank you.