Yeah, mainly on Free Roam. I usually get more players on Free Roam on IV then TBOGT and TLAD.
I only got Xbox Live the beginning of this year, I found a GTA Race with only 3 people and I believe it was a hacked game. If you send a couple messages to some people on free roam, I'm sure they won't hesitate to join .
People still play FM GTA IV on the 360. Sometimes though, there will be people that freeze the game, or play in "God Mode". You cant shoot them or damage their vehicle, but you may explode or burst into flames at any moment.