How do you interact with celebrities? "Attempt Introduction" Failures

I found I have better luck if I do all the other fan interactions first (autograph, selfie, etc) and then try Attempt Introduction. That works about at least half of the time for me. Another great way is to hang out at a bar that a celeb is visiting because the sims who sit on barstools all eventually seem to enter in one big conversation if they all linger enough. Make sure there is not much to do on the lot but visit the bar.