Send them invites for your webinars or whitepapers. Send an email regarding it, and wait for their response on it.
webinar don't always attend the webinar. Adopt measures to convert these registrants to attendees.
How to take advantage of remarketing of your webinar
To simply run a webinar, there are options available like GoToWebinar, GatherPlace, Freebinar, WebEx and many more. All you need to do is set a date for the webinar and send invitees a link to a sign-up page.
Tips to make your webinar more successful