Read this support article about what to do if a iPhone or iPad is lost or stolen -->
Find your lost iPhone or iPad - Apple Support
If Find My iPhone is offline or not working, read this Apple Support article to get help; e.g., when you don't see your device listed, or you see an unexpected device or an alert that says your device is offline. --> If Find My is offline or not working - Apple Support
To me it sounds like the thieves not only stole his phone but also managed to get into his account. While the phone may not be showing in Find My for a variety of reasons such as no longer being charged, it is possible the thieves reset it (Apple does have a bunch of features to deter this but you have to have set them up beforehand). If they have control of his account and possession of the iPhone itself there is basically nothing you can do. I have never heard of a "suspended" message from Apple. If you are paraphrasing, it helps to not do that when posting here but to quote error messages exactly. If Apple has closed the account it may mean they detected unusual activity with the account that caused them to do this.
Read this document if you think your Apple ID has been compromised. --> If you think your Apple Account has been compromised - Apple Support
For iOS 15 or earlier, if you want to see if anyone else has access to your device or accounts, click here --> Checklist 1: Limit device and account access - Apple Support
For iOS 16 or later see how Safety Check on iPhone works to keep you safe. Safety Check for an iPhone with iOS 16 or later - Apple Support
Use the information in this document to check your Apple ID device list to find where you're signed in --> Check your Apple Account device list to find where you’re signed in - Apple Support
Related materials:
Personal Safety User Guide
Personal Safety User Guide - Apple Support
> open the Table of Contents and review the articles
A document with general information about security and your Apple ID --> Security and your Apple Account - Apple Support
Contact Apple for help with Apple ID account security. This page provides country-specific Apple Support contact information ➞ Contact Apple for support and service - Apple Support
About Stolen Device Protection for iPhone - Apple Support