Any type of crime like leaking, checking personal or general information with the help of computer and internet is called cyber crime. Blue whale game is the latest example of cyber crime against society. At large scale teen age group children did suicide without any reason. Daily Newspaper is filled with news of different cybercrime including cheating in exams, bank robbery, copying research paper etc. Government has taken step to stop the cyber crime by making IT Act 2000. The main objective of Research was to find out the knowledge of cyber crime among teenagers using internet. Three hundred samples using internet were randomly selected for the study. A preliminary investigation was taken by the researcher. The structured questionnaire of Dr. S. Rajasekar was used to complete the task. Most of the teenagers do cyber offence without knowledge. There are different ways to overcome cyber crime by making different policies. Results indicates that teenagers using internet has less knowledge about cyber crime. Even they are doing some type of cyber crime without knowledge.