flowtop: 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/flowtop - from package: netsniff-ng

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

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