You have to understand that any ethical social worker or mental health professional will be scrupulous about observing confidentiality. My dad had and one of my brothers has mental health issues, I've interacted with their social workers, counselors, psychiatrists, and others in the field.
Your social worker should be able to point you and your adult son towards resources that can be used to help him, such as mental health centers, counselling programs, public assistance programs. He/she should be able to tell you, as parents, what the limits on things you can do are. My dad was bipolar and his social worker was able to advise us how best to interact with the police and the county psychiatric evaluation team to have him involuntarily hospitalized, and then how to proceed to make the 5150 hold (72 hour evaluation) turned into a two-week hospitalization.
What the social worker cannot/should not be able to do without your son's permission is divulge details on his diagnosis, recommended treatment, details of therapy, or other information that could be regarded as personal and privileged.
FWIW, your son's social worker will be assessing you, at the same time you are assessing him/her. He/she is going to make an appraisal of how helpful you are likely to be, how much you know about dealing with mental health issues, whether you are reasonable, rational people who are still involved in and concerned about your son's life. (Many parents of adult children with mental illness basically "check out" of their children's lives over time, partly because they burn out, partly out of self-defense if their child presents overt dangers to the family, and partly out of sheer rage and frustration that comes with dealing with the mentally ill who resist accepting help or even that they have a problem.) If your son's social worker finds that you are willing to listen, to be educated, to accept that there are limits to what can legally be done, and that you are not going to make his/her job harder, the social worker will be more willing to work with you within the limits of what can be done.
What you can do to assist your child is, first of all, to recognize that there are clear legal limits to what you can do. Dealing with an adult who is mentally ill and in denial can be like stepping into "Alice through the looking glass" into a topsy-turvy world where you have sane, rational people pleading with insane, irrational people to please please please get help. Sometimes, however much it hurts, you have to step back and let the person go "splat" and hit bottom, just praying that they don't take someone else with them and that once they hit bottom there will be some pieces you can pick up to help get them back together.
Your social worker should be able to point you towards support groups in your area, but if he/she can't, try contacting NAMI to see if they have a local chapter. http://www.nami.org/