Hmmmm. I actually disagree with this comment.
I think that signal is a useful alternative for people that are privacy oriented or that do not have an existing chat, but to make the transition from Instagram to signal is going to feel like a step back for the vast majority of normal users especially teenagers/preteens.
On a related note, because we do not know the age of the original poster, it is a non-starter to say that his parents should not be tracking his whereabouts until we have more information. For all we know, this could be a 13 year old. I'm more useful alternative would be to suggest privacy-friendly location apps