When episode 4 came out, people saw the trailer at the cinema before the regular feature, that was it.
When episode 1 came out, people again saw the trailer at the cinema, but I think it was also on tv shows as the actors and George Lucas did the media promotion rounds. Not sure if it was available online, media companies were much more cagey about sharing stuff in those days. Plus people would have had to contend with dial-up speed. If I looked around, may be some geek would have posted about it on the then brand new livejournal site.
Episode 7 is coming out next year. The first teaser, on the official youtube channel has been viewed 9 million times as of today, and shared an enormous number of times on social media. Everyone watched it multiple times within minutes, hours of it being released. Each frame has been scrutinised and dissected. There are even fan adaptations, like this lego version, itself with 1 million views.
I must admit, I love it. It feels much more like classic ep 4-7 than stupid ep 1-3. Stormtroopers, X-wings, a Tatooine-like landscape, new faces that don’t look annoying, and look at that lightsaber! (still prefer Darth Maul’s double sided one.) I can’t not share this, right? One more year to wait.