Send an email (or hand written note if you have an address available to you)thanking them and telling them what a great time you had and that you are still very interested in them.If you hear back from them keep the lines of communication open.Invite someone that you clicked with out for lunch or a drink or something.There were women that I met at the first alumnae meeting that I would have continued to be friends with even if we didn't have the Alpha Phi connection.If you don't hear from them right away, over the course of the summer just send them a gentle follow up reminder or two that you are still here and interested.Schedules get crazy during the summer and it might seem like they aren't interested if you don't hear from them right away but they just might be busy.I would say that maybe one email a month is fine and PITA free.