Some more thoughts, OP, born from personal experience.
1.Lean in as much as you can to the relationship with your kid - and concentrate on being loving and curious.
- Focus on activities or projects that simultaneously bring you together and your kid away from the Internet. There are some creepy people on there who have quite possibly told your kid that any current discomfort is due to them 'being trans' rather than any other issue in their life. My oldest was effectively groomed in a Pokemon Discord server into thinking they were trans.
3.There is really no rush to medicalise a teenager's discomfort ie don't feel you need to take your kid to the GP or find a therapist immediately, unless you think they are unwell. The teenage years are a tough time for all, particularly if kids are not neurotypical, so there are lots of questions you can explore as a family in the meantime. And sometimes having doctors potentially affirm this stuff reifies it and does not let it pass as it most probably will.
4.Encourage your teen into any activity that they enjoy and which helps them feel embodied rather than disassociated from their physical selves.
- A sudden announcement of trans identity in the teens which runs entirely counter to how the kid has always been is, I think, pretty much nothing to do with their 'gender'.
In my experience, there are real issues at play but they are almost certainly not about gender. Rather, these kids are fearful or anxious about something: growing up, other kids' attitudes, feeling they don't fit in, worries about moving on, their emerging sexuality or changing body, porn, a trauma response, lack of control, not feeling seen, insufficient attention within the family, being a privileged person etc etc etc
At this point in time, our culture both encourages and misinterprets this way of expressing distress...
- It is overwhelming and exhausting dealing with this stuff but your kid will pick up on this and is possibly looking out for 'hostility' as they are encouraged to do by people who don't give a monkeys about their well-being (as we have seen evidenced on the thread) so try to carry on being as loving and engaged as you obviously are.
7.Remember, You are the expert on your child at this point, not teachers, not health professionals, not randoms on the internet.
- Try to get other family members to understand your position and your strategies for dealing with this so there is no undermining or splitting
- Practice self care and find someone to vent to irl with whom you can be 100% truthful about how you feel.
10.There is plenty of time and no rush to do anything. It is a marathon and not a sprint. Join groups like Bayswater, gender critical resources etc to get support from other parents going through the same thing.