I was around in the 70s and 80s. I'm well aware of the limited technology we had and what a slow pace it operated with. As far as telecommunications, there were telegraphs, landline phones, and snail mail to keep in touch. If you lost a person's phone number and address, you essentially lost that person. I know from experience, as a teen, losing track of friends in the early 80s, who moved out of state. My sister read my mail and lost the envelope with one of my friend's address on it. And she was gone forever in my life. But I began searching for them with the internet as soon as it became an option, with what information I remembered. And then used social media when it became a thing. One friend I found, two I haven't. But I keep looking.
For media, there was newspapers, magazines, radios, and television. Oh, and ham radios and CBs. None very conducive to finding people, short of taking out classifieds in the print media, and news broadcasts, there wasn't much, but still there. I totally get options were limited when it came to putting the word out about a missing child, because that's what we're talking about here, a child, and staying connected, but they were there. And they were limited when it came to searching.
One of the first missing child cases I remember as a child was Adam Walsh, who went missing in 1981. It was big news, at least to me, and then shortly after, the milk cartons came out, too. Then NCMEC was created in 1984. Specifically for missing children. New resources at someone's disposal with missing children, for free, I believe. Yes, resources to search for and get the word out about a missing child were limited and slow, but not nonexistent. Not inaccessible, and, not unknown.