I’ve found LinkedIn to be a reliable method for a first contact.
You can always try to e-mail me, but the machine learning algorithm behind my anti-spam services has a dislike for unknown persons suddenly writing me: their messages often end up in the spam folder. Anyway, if you want to try your luck, e-mail me at: Luca (at) cybersecurity _dot_ it
Twitter could be a method as well as my DMs are open. Though unless I follow you, your message would end up in the “message requests” folder and I would not get notified.