How would I make it so I have many enemys but then when one sees the player it sends a message to a manager that he saw the player(I know how to do this part). Though when the manager receives the message it sends a new message to all of the enemys, with a vector3 sent when one enemy saw the player.
Google for the Observer Pattern.
I see you understand what approximately you want to do, so why then asking for help?
Just google each separate part and there are dozens of examples. And if there is no specif purpose for using sendmessage, use getcomponent instead.