WhitePages.com (best)
Spokeo.com (find them at an EP address, then check other addresses to hopefully find a current one)
Refer to graduation commencement program for full names, including middle name for searching.
Create a Google Form (or here) for them to fill out their information.
This will create a spreadsheet in Google Drive that you can transfer their information to Google Contacts. The spreadsheet can be shared privately with other reunion committee members.
(Note: Input contacts by their high school name (maiden) for easier recognition by former classmates. Use "nickname" option for their current married name.)
Request classmates email address, preferably a Gmail, Hotmail, Yahoo email; the cable/phone company ("comcast") ones may become obsolete if they move.