Q. You mention using the internet to find out how to contact people and I was wondering what is the proper way to contact people who I heard giving lectures at the Screenwriting Expo? I don’t want to ask for a job or for them to read my script, I just wish to thank them and ask them follow-up questions. Is it better to go through their agent or the TV show that they work on?
If you just want to thank them, send'em a postcard at their show. They'll appreciate it. They probably do not want to be asked follow-up questions, and their show and their agent will generally try and stop you from contacting them with stuff that will not result in a paycheck. (Especially the agent.) But if you can smoke out their email, feel free to try.
When I was talking about using the Internet, I meant using it to find like minded aspiring filmmakers you can work with. Best to leave the professionals alone, unless they've indicated they're willing to talk to the outside world -- e.g. they have comments enabled on their blog, or publish their email address.