Let's assume an arbitrary group of people who hold a key pair and who make their public key online accessible.
Let X, A, B and C be arbitrary people from that group.
Now X wants to encrypt a message once using A's, B's and C's public key so that only A, B and C will be able to decrypt the same ciphertext.
(Think of an encrypted FB/Diaspora where you would like to introduce asymmetric encryption but don't want to encrypt individually for each of your friends. And the content might be stored centralized - such that more people from the total user group have access to the data but shouldn't be able to decrypt it.)
Is that technically possible? If yes, does this asymmetric encryption method already have a name or known implementation?