Personally, I would say that they're effective, however, they are also unethical. Teens typically don't know what's best for them, and they also don't have the finances to purchase such tech products. But, because naturally advertisements are meant to be convincing, if done well, it can convince teens to do what they need to in order to afford these products. An example could be Apple advertising the newest iPhone or Macbook to teenagers. These are very expensive products, but the moment that they are released everyone wants them, so yes it is effective. However, teenagers are very impressionable. One again, they don't know what's best for them or what they actually need. Companies are actively preying on teens' vulnerability and desire to own things they think are "cool," therefore advertising tech products directly to the youth for monetary gain is unethical.
