ftpasswd: 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/bin/ftpasswd - from package: proftpd-utils

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

On Debian possible default full paths are:

/usr/sbin/ftpasswd - from package: proftpd-basic

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

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