Whois still works. Try it:

    > whois ycombinator.com
    Domain Name: ycombinator.com
    [snip]
    Admin Name: REDACTED FOR PRIVACY
    [snip]
    Admin Email: 1bd279b6ad24fb60b2e200db8f486c3f-2545852@contact.gandi.net

Gandi.net will get the message through to the person who would have been registered as the admin contact.