there are a few websites devoted to crew keeping in touch, but I have never been on to any of them. most crew keep in touch through personal email and the ever existing grapevine. ships are a small world and I always run into someone who knows someone or people from the past.
you always haver to remember that ships are very transient so younever know from contract to contract who will go who will stay...and who moves to another line or company.
all ships now have internet cafes, and they are well used by the crew during breaks and off time. keep in mind though that internet time at sea is still more expensive for crew than on land. there are many spots that dedicate thier buisness to being available to crrew members at a very reasonable rate.
hope this answers your questions