Almost over night people were switching to (or adopting) MSNM, often reproducing online the cliques already existing in the local communities.
I think AIM was only ever popular in the US (America On Line after all).
The interesting period was when IRC was still popular even among non-techies. The girls in school would sit on the PCs in mIRC.
ICQ at school was really cliquey there was a lot of "I'm going to give you my ICQ number but you can't give it to X".
Teenage me was really happy when I got the ICQ # of a girl at school I had a huge crush on (This was pre mobile phones so you couldn't exchange text messages back then or snap chats or whatever the kids use to flirt with each other these days).
When I moved away from home and started university I stopped logging in lost touch with a heap of people as a result. I can't remember my ICQ no. nowadays...