mpicxx: 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/mpicxx - from package: mpich2-devel
/usr/lib64/mpich2/bin/mpicxx - from package: mpich2-devel
/usr/lib/mpich2/bin/mpicxx - from package: mpich2-devel
/usr/lib64/mpich/bin/mpicxx - from package: mpich-devel
/usr/lib/mpich/bin/mpicxx - from package: mpich-devel
/usr/lib64/mvapich2/bin/mpicxx - from package: mvapich2-devel
/usr/lib/mvapich2/bin/mpicxx - from package: mvapich2-devel
/usr/lib64/mvapich2-psm/bin/mpicxx - from package: mvapich2-psm-devel
/usr/lib64/mvapich/bin/mpicxx - from package: mvapich-devel
/usr/lib/mvapich/bin/mpicxx - from package: mvapich-devel
/usr/lib64/mvapich-psm/bin/mpicxx - from package: mvapich-psm-devel

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

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