There are different types of therapy.

Cognitiive behavioural - identify how the ways in which you think drive your emotions and learn to question your thoughts

Psychotherapy (often mixed with some cognitive behavioural nowadays) - identify why you think the way you do before learning to question your thoughts (this is useful for people who find it difficult to question their thoughts or who blame themselves for having the thoughts in the first place, or who know the thoughts are irrational but believe them anyway - it puts the thoughts into context so that when you're inundated with self criticism you can't shake you can use self-compassion - "of course I feel bad with all this criticism going on in my head, and of course I can't help being so self-critical when I was brought up in an environment where I was constantly criticised - this isn't nice for me at all, I'm going to choose to be extra kind to myself to help get me through it")

Mindfulness-based - Creating distance between yours and your thoughts and emotions so you can recognise they are transitory and not get 'stuck' in them, fueling the fire, making it easier to let go of what's happening in your mind

Group therapy - For people who experience problems in their relationships with others. Usually a long-term therapy that allows people to gain first-hand experience of other people (who aren't being paid...) accepting them for who they are, caring about their welfare, being trustworthy and non-abusive etc. so that the patient can learn over time that not everyone will abuse them/criticse them/judge them/neglect them etc. with the hope they're then able to trust people more outside of the therapy room. In individual therapy, it's easy to tell yourself that the therapist is kind because that's their job. In group therapy, the other patients don't have to be kind, they can just choose to be. It's also good for teaching people to face conflict. Facilitated by the group leader, patients are encouraged to be more honest and open about their feelings and thoughts so they can navigate conflict and learn that it is safe, therefore hopefully feeling safer to face conflict IRL.

Normally, therapy is a mix of all the above things. But the goal is for the person to recognise how their internal processes are fuelling their unhappiness (through no fault of their own) and make changes to the way they internally process life so they can experience more positives.

Source: Patient who has had all the above 'types' of therapy in various guises and has found it helpful.

There are a lot of difficult things about parenting teens (I imagine, I don't have kids yet *crosses fingers for kids pre-menopause....*) But I'm not sure this is one of them. Kids often start masturbating as very young children - toddler age, sometimes - and this is a normal thing for them to do. At that age, of course, it's not associated with sex for them, they've just found a body part that feels nice. Any decent parent explains privacy to a young child but does not shame them for being a human being and lets them get on with it.

Once your child has reached puberty, if you don't completely expect that your child is masturbating then I don't know what's wrong with you. Of course they are. If you come across their masturbation aid (regardless if it's a toy or porn) then just put it back where you found it and don't mention it!