Like in-person events, you have to think about how you can get some buzz for your upcoming webinar. You can do it through different digital channels like ads on different social media platforms. You can do the same through YouTube, or run paid ads in search engines like Google and Bing. And surprisingly, you can also use traditional advertising, like TV and radio ads, printed posters, and brochures, to promote these web seminars.
Just like how in-person events don't limit themselves to non-digital platforms, webinars shouldn’t be limited to digital promotion.
The only limit should be your imagination (and your budget; but it’s nothing good old creativity couldn’t overcome).