1) Please ensure that $ORACLE_HOME/lib is in the $LD_LIBRARY_PATH
2) As Mark mentioned, a 32bit Oracle Client is required, and if the Oracle DB is on the same host, then ensure the 32bit path is ahead of the 64bit path for $ORACLE_HOME/lib in $LD_LIBRARY_PATH.
3) By default Oracle Client installation may not create the libclntsh.so symbolic click to the libclntsh.so.<major_ver>.<minor_ver>. You may have to create this by hand.
# ls -l /u01/app/oracle/product/12.1.0/client_1/libclntsh.so*
lrwxrwxrwx 1 oracle oinstall 17 Jul 30 13:36 /u01/app/oracle/product/11.2.0/client_1/libclntsh.so -> libclntsh.so.11.2
-rw-r--r-- 1 oracle oinstall 43022035 May 27 2013 /u01/app/oracle/product/11.2.0/client_1/libclntsh.so.11.2
Cheers,
Chandru