creating a users list for eatch user (chat app)

    i have made a chat app and i want to let the user add another users that he can find by searching the database of users to his own list, and grouping them ,,, this is can be done

but ,,, now in my app when the user connect to the lobby he get all the online connected users in his list i mean when connecting to the online user list sharedobject the user list contains all the connected clients to the lobby and if the number of the connected users is by hundreds or thousands i think

if i create a loop for updating the own user users list statues it would not be good idea,,,

so what is the best way to let the user build his own users list and get the statues of each user in his list from the application online users sharedObject witch connected to the lobby app