There are two mailing lists you can ask for support:
Note: Before sending email to a list, you must be subscribed to it. This is due to the amount of spam received and the administrative burden it was causing.
These mailing lists are specifically for the Nagios Plugins. If you have a question about Nagios (or NRPE, NSCA or NDOutils), see here for the relevant lists.
You can find archives of the nagiosplug-help and nagiosplug-devel mailing lists at gmane.org.
Be aware that these mailing lists are read by volunteers, so responses may take time, if at all.
There is an IRC channel, #Nagios at irc.freenode.net, where the topic is anything about Nagios.