Networking with Non-Alumni

Just had a couple of quick questions in regard to networking with random non-alum. I come from a school with a decent alumni presence in banking but I'm looking to expand my network to increase my odds and get a feel for different bank cultures. My question is what is the most successful way you all have gotten connected with random non-alum other than from referrals? Also, what subject line do you use when cold emailing? I know if there is an easy connection like sports or hometown or stuff like that, but I'm not sure what to do if we have nothing in common. I would appreciate any input from current students that have experience with this or any bankers on the opposite side. Thanks.