I will tell you what my brother has done. Last year he got interested and he and his brother inlaw bought karts after renting karts several times. He then got me interested and eventually my dad so interfered that he bought a kart too (although is too intimidated to actually race).
He just got his 2 young boys involved and now they race.
He has taken our cousin out, who has now raced just a couple weekends ago and might buy a kart in near future.
He has also taken at least 3 or 4 other friends and their kids out. Most just have a good time for the day of practice, while others contemplate buying karts.
I have taken a couple friends out and have invitations for another. I thought I had one guy hooked, but I think money is a factor.