libtool installed but not found in /usr/bin

They're not the same thing, libtoolize is part of libtool.

From this link (http://www.gnu.org/software/libtool/manual/html_node/Invoking-libtoolize.html):

The libtoolize program provides a standard way to add libtool support to your package. In the future, it may implement better usage checking, or other features to make libtool even easier to use.

I ran into this same problem today on a Debian system and (eventually) discovered that though the libtool package was installed, the libtool-bin package was not.

apt-get install libtool-bin

Problem solved: which libtool prints /usr/bin/libtool.