Where to put VirtualHost files for brew's httpd24?
You have to edit the file /usr/local/etc/apache2/2.4/httpd.conf.

Search for and uncomment the following two lines (remove the # at the beginning of the line):

#LoadModule vhost_alias_module libexec/mod_vhost_alias.so
#Include /usr/local/etc/apache2/2.4/extra/httpd-vhosts.conf


Then edit the file /usr/local/etc/apache2/2.4/extra/httpd-vhosts.conf to suit your needs.