rabbitmq-plugins: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/lib/rabbitmq/bin/rabbitmq-plugins - from package: rabbitmq-server
/usr/lib/rabbitmq/lib/rabbitmq_server-3.1.5/sbin/rabbitmq-plugins - from package: rabbitmq-server

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/lib/rabbitmq/bin/rabbitmq-plugins - from package: rabbitmq-server
/usr/lib/rabbitmq/lib/rabbitmq_server-3.3.5/sbin/rabbitmq-plugins - from package: rabbitmq-server
/usr/sbin/rabbitmq-plugins - from package: rabbitmq-server

You may install the required package with command apt-get install {package}

Error in other languages:
rabbitmq-plugins: bevel nie gevind nie
rabbitmq-plugins: comandă negăsită
rabbitmq-plugins: comando não encontrado
rabbitmq-plugins: commande introuvable
rabbitmq-plugins: command not found
rabbitmq-plugins: käsku ei ole
rabbitmq-plugins: không tìm thấy lệnh
rabbitmq-plugins: komanda nerasta
rabbitmq-plugins: Kommando nicht gefunden.
rabbitmq-plugins: kommandot finns inte
rabbitmq-plugins: komut yok
rabbitmq-plugins: nie znaleziono polecenia
rabbitmq-plugins: níor aimsíodh an t-ordú
rabbitmq-plugins: no se encontró la orden
rabbitmq-plugins: no s'ha trobat l'ordre
rabbitmq-plugins: opdracht niet gevonden
rabbitmq-plugins: parancs nem található
rabbitmq-plugins: perintah tidak ditemukan
rabbitmq-plugins: príkaz nenájdený
rabbitmq-plugins: příkaz nenalezen
rabbitmq-plugins: команда не найдена
rabbitmq-plugins: командата не е открита
rabbitmq-plugins: 命令找不到
rabbitmq-plugins: コマンドが見つかりません