You cannot access it remotely, but you can wipe it clean remotely and/or set a new password. If your phone was backing up nightly automatically, you should be able to get all that information back on restoring to a new device. You might want to use the find feature to see where it is and then share that information with law enforcement. However, the first thing you want to do now, is log out of both your Google and Samsung account, you don't want anyone accessing those accounts or being able to use the phone while it's still logged in.
If you log it out of your account at least your accounts are safe. And you will still be able to set a password to the next time somebody boots it up they'll be an additional password on the phone. You're supposed to be able to locate it even when offline I don't know if that includes being dead but I made that assumption. I don't know how it works though.
