In the 70s there were lots of good kids from good caring families who were out on the road seeing the world, hanging out in cool places like SF or LA, in touch with their families but not that often.
It was hard to keep track of each other in the days before cell phones. Letters, postcards, took a long time. For the phone, you had to have enough money to make a long distance phone call, and you had to take the chance on whether anybody at the other end was going to be there to answer, because answering machines were just coming into use. And it was expensive just having a phone, so lots of people, especially in rural areas, didn't have one. They used a pay phone when they needed to make a call.
If there was some coolness because of lifestyle choices or something, that made it even harder.
If someone was traveling, the family back home might not even know where to start looking, or might be looking in the wrong place.