Most of us under communicate. In many of our valuable UNNATURAL relationships ( the ones that are NOT in our weekly lives; i.e. home, work, school, church, etc ) these relationships are likely malnurished.
If asked, we would say that we wished we kept in touch with so-and-so on a regular basis. So my suggestion is that you start spamming them.
Yeah- spammers don’t wait for invitations or requests. They just blast out their message to people at all times and all seasons. So you should start sending friends unsolicited messages via email, voice mail, and snail mail.
Whether they return them or not; impose on your friends love, kindness and concern. And be the friend that you would want whether the relationship comes natural or not.