I join GROUP giveaways and I'm actually the organizer of the one that is starting on Sunday. because it's a group, we are all responsible to advertise it!
And trust me everyone, including the smaller blogs, want to advertise the giveaway because they know that it drives alot of traffic!
I also use all of my social sites and post about the giveaway! Last month alone I was in a twitter giveaway and I went from having 240 to having 900! that's a 660 follower jump in less than 2weeks!