I think that the first step for you and your son is to discuss what he's truly interested in, what he knows he's good at and what is important to him. Exploring what his interests are and what he likes to do will lead to a discussion of what jobs or careers are a good fit for those interests. Are there specific classes he excelled in? Are there hobbies that he's very involved in? Even things like enjoying cooking or repairing electronic equipment can give clues as to possible careers or jobs that he would enjoy. He can apprentice himself to someone whose job and field of work interests him. He can explore internships, paid and unpaid, in corporations. He should definitely go to his guidance office and use the books and resources they have to help him identify non-college courses of action. The guidance office should also be able to recommend good "career inventory tests" which they can administer. There are also professional vocational and career counselors who could work one-on-one with him. Ask his guidance counselors to help you find one of these counselors who would be a good fit for him.
But What if I Don't Want to Go to College, by Harlow Unger is a fine book that details hundreds of career opportunities obtained through vocational education or other alternative, non-college training. Your son does not need to feel like a "loser" because he is not going to college at this time of his life. However, he does need to realize that he can't graduate high school and expect to lounge around the house indefinitely. Rather than focusing on what he's not going to be doing after high school (especially since this is the time when kids are applying for college), he needs to have his desires respected and his energies directed toward what he's going to try out after high school. He may not be considering college because he's tired of going to school or because he thinks he would not succeed in college. It would be helpful if he could talk with someone he respected about the real reasons why he's confused and/or uncertain about "life after high school."
He needs something to look forward to and to get excited about after he graduates. Between now and when he graduates, I hope that you can encourage him and assist him in following through on some of my suggestions.