Dear NG,
I am not an expert on this topic but there might be some data protection concerns as to storing personal data of 3rd parties that are to be contacted in case we miss someone.
What i do know is that when you send a personal message on NG, an automated notification/email is generated and send to the recipient.
At the moment I don't see what else NG can do to reach Mike G.
I certainly hope that Mike G is healthy and that he will reappear in the near future.
Yours, Jakov