I have recently moved over from SteamOS which is Debian Wheazy. None of the other fixes have not worked, I tried getting steam both through Steam itself and the Ubuntu Center.
Assuming libc.so.6 is the only one you are missing, open a terminal and execute the following commands to install the missing library (be careful here and do not accept changes unless you are happy with the changes ie may uninstall stuff you want to keep!!):
sudo apt-get update sudo apt-get install libc6-i386
Please post any errors.
If like me, mchid answer didn't solved your issue, try making a symlink to libc.so.6 and reinstalling steam from steamcmd:
find /lib -name libc.so.6 ln -s /lib/i386-linux-gnu/libc.so.6 /lib/libc.so.6 mkdir ~/steamcmd2 && cd $_ wget http://media.steampowered.com/client/steamcmd_linux.tar.gz tar -xvzf steamcmd_linux.tar.gz ./steamcmd.sh