This can be done with a plugin or (probably easier) Lua script. Limitation being that it will only work if you are subscribed to the channel in which the people you're looking for are connecting to / located in.
In other words, it won't work if they connect to a channel which you cannot subscribe to and thus don't know who is inside those channels. For general channels it will work fine.
When sending PMs please make sure to include a reference link to the thread in question in the body of your message.