Teenagers aren't getting pregnant because they want to be on Teen Mom 3. It's just not happening. In fact, teenage pregnancy rates are dropping in the United States.
There is some evidence that teenagers do try to do stunts like the ones on Jackass or Ridiculousness, but that's more of a YouTube thing than a TV show thing at this point in time. I'm all for getting some of these awful reality shows off the air, but I don't think there is any evidence that they're creating imitators in real life.
These days there are alot of behind the scenes episodes showing how reality shows work. I don't think they are as easily influenced by the shows because they can understand that it is just for entertainment. Inappropriate behavior is mainly influenced by the atmosphere in a teens house, although school can also be a source of a child's behavior as well