Teen Son Starting Marijuana

My 16 year old son has begun taking drugs about a month ago after making new friends since our move. He has quickly went from just a couple of times to 4 times a week. My husband and I have had contless talks with him to no evail. So I contacted the school counselour but still he continues to use mariuana. Now I dont know what step to take next. He is very open about his use with us and does not see a problem. I need some advice with where do we go from here.
I too have a 16 yr old son. I sent him to live with his father last sept. He went from bad to worse, he is also very open about his pot smoking. His father reports that he leaves all evidence throughout his house and has even damaged furniture etc..he is totally out of control..he has gone through 3 high schools since sept. of last yr. mainly because his dad moved. Please, if anybody has any suggestions on how to help my son it would greatly be appreciated...first step is to get him back with us.