Linkedin Messaging vs Email

Hey guys, I'm a rising sophomore non-target student who just started networking for IB/Consulting. My school has a somewhat vast alumni database given our size, but I haven't found the emails of many people - I'll run it through an email checker with no sucess, even if I look up the format online. I resorted to linkedin messaging - seen a few good things about it on here, but I would prefer emailing. Any advice going forward?