chcuk when I run whereis whereis on one of the machines I am handy to I get
[root@machine:/root]# whereis whereis
whereis: /usr/bin/whereis /usr/share/man/man1/whereis.1.gz
perhaps /usr/bin is not in your path?
Look at your .bash_profile if you're running bash.
PATH=$PATH:$HOME/bin:/usr/local/bin
Add more to it as you feel necessary, colon delimited. log out, log in. magic. Now it will start finding things for you.