I was Student Govt President when I was in high school & I also chaired our 10 year reunion committee. Coincidentally, I was also teaching at my old high school.
People contacted me to help out w/ the committee & early on, we decided to hire a company who specialized in reunion planning. (
www.reunited.com - I think they're just FL based.) We had a class of 650 & everyone was in early-mid career, so it worked out fine, since they did all the grunt work of finding people.
My sister (who was also SG pres her year) just had her 20th & used the company we used & she felt it was a rip off. But at least she has a solid list of alumni to plan their 25th.
BTW, my sister is a KD - yes, I suppose I was one of those sisters who copied everything my sister did. But I think it ended at pledging KD!
Good luck!