I'm a full-time traveler these days and my wife and I have probably met around 10 couples (actual offline meetings) via Instagram.

Facebook is more for people you know. (Filled with babies and relatives.. etc) where Instagram has been great for finding like minded folks and following along with their lives in short snippets.

As for how to communicate, Instagram has user tagging. Even in others comments. Basically the same as sms messaging.

( My wife has more followers than me and I need to catch up: http://instagram.com/wandering_tim )