no such process error with launchctl start. Mac OSX 10.9
Try using the launchctl command:

launchctl load /Library/LaunchAgents/com.myfile.hostname.plist

This will load the job ticket rather than start a named job.

I am not sure pipes are permitted within a launchd job ticket list of arguments. Using them requires the argument to be passed to a shell for interpretation and this may not happen. Consider passing the command directly to /bin/sh as a single argument.