Just use whatever contact they have on the website. Dear <company> website team, I am a security consultant for <my new company I made 10 seconds ago>. While

Just use whatever contact they have on the website. Dear <company> website team, I am a security consultant for <my new company I made 10 seconds ago>. While casually visiting your site, I recently found a severe security bug that not only leaks private information, but has the potential to alter a user's reservations. Please contact me as soon as possible so I can let your technical team know about the problem (no charge, of course). Thanks, Me Security Consultant, <new company> <phone #> Might as well try to get some business out of it ;-)