Be careful where people recommend you send your boy as off the derech means many different things, from a boy who does not want to daven to someone with serious drug related problems.
I relate to the post of Zahavasdad because I think when a young person is seen going off the derech they are not necessarily seeking to reject Torah values , but perhaps turning away from the tribal conformity which dominates so many communities. As I have said elsewhere, often the brightest kids can go otd. Bright kids do not like being forced not to think, they also can see through some of the hypocrisy that exists around them and get a perverse pleasure in playing the system.
I write from the other end of the spectrum, I am a Modern Orthodox mother with quite a few kids, and one of my sons turned out to be a real rebel, he insisted on going to a litvish yeshiva, wears only black and white complete with a smart big black hat on shabbat/Yom Tov. He gave away his jeans in exchange for a monochrome wardrobe which broke my heart for what it symbolised to me, a strong dati leumi ima, until I realised what HE is, my son, not a mere member of somebody’s yeshiva or shul, my flesh and blood. I realised his life is not about fulfilling my expectations but his, he made those decisions as a teenager and now as a young man he is at the heart of our family. It is hard not to worry about what your community thinks, but most of all worry about what your son thinks about you, his family. If he sees honesty, true emunah and yiddishkeit from home, he will acknowledge the difference between what he is rebelling at the moment, and what he actually has deep down. You should be firm about halachot and your standards of yiddishkeit, but do not be intimidated by the community around you. If his RY has lost students then others too have fled the yeshiva for their own issues, your son is not alone, remember a yeshiva is not a mere place for education, it is a place of spiritual development, positive or G-d forbid, negative if undertaken by the wrong people.
Do not worry about what others think, in truth the number of families with difficult circumstances to contend with is very high, nobody talks about it, people only like to talk in public about their great achievements, not their challenges.
I teach in a big educational establishment with many young men and women from frum backgrounds seeking professional qualifications, you would be surprised to realise how many of those who have been the most interesting and successful students had a hard time as teenagers, went to various yeshivas and sems, and then took their challenging experiences with them to make postive changes to their own lives. He is your son and you love him, disregard concerns about image and focus on truth, he may surprise you with his response.