localhost / userdir on macOS Sierra
There is an updated tutorial here: How to Set up Apache in macOS Sierra 10.12
It includes extra configurations like uncommenting the following lines by removing the "#":
#LoadModule userdir_module libexec/apache2/mod_userdir.so
...
#LoadModule vhost_alias_module libexec/apache2/mod_vhost_alias.so
...
#Include /private/etc/apache2/extra/httpd-userdir.conf
...
#Include /private/etc/apache2/extra/httpd-vhosts.conf
in /etc/apache2/httpd.conf
and uncommenting:
#Include /private/etc/apache2/users/*.conf
in /etc/apache2/extra/httpd-userdir.conf
and restarting apache: sudo apachectl restart
It should work.