Teenagers who have been thinking about death will generally speak about it. What you need to do is get direct with your child and ask them the reason for their interest in death. If they glorify it or state it as a remedy for all problems in life then take that as a sign that they may be contemplating hurting themselves. Ask them if they have any problems that can be solved only by death. Probe and get to the bottom of what their problem is. Explain to your child that there are always solutions to things in life and death is not a solution to anything. One, because such an extreme step need not be taken to solve life’s small problems. And two, because death itself throws up a completely new set of problems for the loved ones left behind. Tell them that you love them unconditionally and will help them solve all their problems.
If you think your child is still not looking happy, please consult an expert.