Some modern programs requires libc6 version 2.14 or higher. But, original Debian 7.X (Wheezy) contains only libc6 v.2.13 and you getting an error, like my Viber
/opt/viber/Viber: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.15' not found (required by /opt/viber/Viber)
/opt/viber/Viber: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.14' not found (required by /opt/viber/Viber)
But, you can install libc6-alien package and run application in this way:
with-alien-glibc i386 /opt/viber/Viber
architecture: i386 for x86 architecture, or amd64 for x86_64 architecture