Linux – Nothing is written in php5-fpm.log

I have two servers which is Ubuntu 12.04 and Ubuntu 14.04. When I use Ubuntu 14.04 in my new server and enabled the php-fpm log file found under /etc/php5/fpm/php-fpm.conf that reads as follows:

error_log = /var/log/php5-fpm.log

I noticed that most of the log that I found in Ubuntu 12.04 is not written in 14.04. For example, if I restart php5-fpm in my Ubuntu 12.04, a restart log is being written, however, this does not happen in 14.04. Another log which I missed in 14.04 are the following:

[23-Aug-2014 16:23:03] NOTICE: [pool web42] child 118098 exited with code 0 after 12983.480191 seconds from start
[23-Aug-2014 16:23:03] NOTICE: [pool web42] child 147653 started
[23-Aug-2014 17:27:31] WARNING: [pool web8] child 76743, script '/var/www/mysite.com/web/wp-comments-post.php' (request: "POST /wp-comments-post.php") executing too slow (12.923022 sec), logging

I really wanted to have this kind of log so I will know the length of time a slow script has executed.

Does anyone know if there are other settings in Ubuntu 14.04 that I need to change in addition to /etc/php5/fpm/php-fpm.conf?

Update:

This is the result when I run /etc/init.d/php5-fpm restart ; find / -type d -name /proc -prune -o -type f -mmin 2 -print:

find: warning: Unix filenames usually don't contain slashes (though pathnames do).  That means that '-name `/proc'' will probably evaluate to false all the time on this system.  You might find the '-wholename' test more useful, or perhaps '-samefile'.  Alternatively, if you are using GNU grep, you could use 'find ... -print0 | grep -FzZ `/proc''.
/var/log/ispconfig/httpd/mysite.net/error.log
/var/www/clients/client1/web4/web/wp-content/cache/page_enhanced/mysite.net/page/12-cool-hybrid/_index.html
/var/www/clients/client1/web11/log/error.log
/var/www/clients/client1/web11/tmp/sess_phi0akqc8k4r6pkqkg26im83i4
/var/www/clients/client1/web11/tmp/sess_vibcotqj4hht6u9boij9mufjs0
/var/www/clients/client1/web11/tmp/sess_lfdh2ol4hotpforolq693hvj70
/var/www/clients/client1/web11/tmp/sess_64slp06h69v35tg6nfq6u1uqm2