To fix this issue follow the same steps (starting with the download of libmemcached-0.25.14.tar.gz) detailed here.
Because the source installation of libmemcached dropped the libs in a non-standard place (from a Debian/Ubuntu viewpoint) we need a little more magic before things will work.
As root, create /etc/ld.so.conf.d/libmemcached.conf:
# Manual installation of libmemcached dropped the libs in a non-standard placeRun ldconfig to load the new config and test to ensure your script can now access libmemcached properly through the memcached gem.
/usr/local/lib