romenigld

I already have libxml2 installed.
but if you don't:
$ brew install libxml2
And I do these steps and works:
$ brew list libxml2
/usr/local/Cellar/libxml2/2.9.7/bin/xml2-config
/usr/local/Cellar/libxml2/2.9.7/bin/xmlcatalog
/usr/local/Cellar/libxml2/2.9.7/bin/xmllint
/usr/local/Cellar/libxml2/2.9.7/include/libxml2/ (47 files)
/usr/local/Cellar/libxml2/2.9.7/lib/libxml2.2.dylib
/usr/local/Cellar/libxml2/2.9.7/lib/cmake/libxml2/libxml2-config.cmake
/usr/local/Cellar/libxml2/2.9.7/lib/pkgconfig/libxml-2.0.pc
/usr/local/Cellar/libxml2/2.9.7/lib/python2.7/ (4 files)
/usr/local/Cellar/libxml2/2.9.7/lib/ (3 other files)
/usr/local/Cellar/libxml2/2.9.7/share/aclocal/libxml.m4
/usr/local/Cellar/libxml2/2.9.7/share/doc/ (153 files)
/usr/local/Cellar/libxml2/2.9.7/share/gtk-doc/ (55 files)
/usr/local/Cellar/libxml2/2.9.7/share/man/ (4 files)
$ sudo ln -s /usr/local/Cellar/libxml2/2.9.7/lib/python2.7/site-packages/* .
$ irb

require 'nokogiri'
=> true