addpasswd: 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 Debian possible default full paths are:

/usr/sbin/addpasswd - from package: gnugk

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

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