To PM someone on the site, including the Admin, you must select their name and then the "mail" tab over their profile.
You can find the name of all staff at the bottom of every page by scrolling down and looking under the "members" column. Select "moderators" and you'll see a list of all of us.
There is also a "report" option under every message you receive. But for a death threat, I would contact the admin directly.
I'm sorry that you've had to experienced such disrespect within the community. I'm sure Pet will handle it quickly and thoroughly.