I see... maybe a loop is required here then.

'domsg' will be the custom msg alias.

Code:
alias domsg {
  var %i = $numtok(%m.ptype,32)
  while %i > 0 {
    var %chan = $gettok(%m.ptype,%i,32)
    if ($me ison %chan) { msg %chan $1- }
    dec %i
  }
}
and use: /scon -at1 domsg MP3 Player online