I was getting some acne on my quads and triceps. I switched my showering to washing those areas as normal, then I put some soap on a loofah and scrubbed the areas mildly (just like 10-20 seconds per area, maybe 30). It took a few days to notice the problem diminishing , but it worked, and I continue using a loofa in the same way even though the problem is gone. I think someone recommended using a loofah when I was going through puberty and getting backne. Glad I remembered that fix.
Also, some guys at the gym wear shorts that have a kind of spandex underlining (I assume to prevent your balls from hanging out). The following link indicates this could be a problem: http://www.womenshealthmag.com/beauty/butt-acne (addressing spandex yoga pants; but please ladies, don't stop wearing yoga pants, you look smoking hot in them).
Finally, I noticed these tips--for women, although I'm sure they are equally applicable to men. I can't say I've used any of the products they refer to, but worth a shot if the above doesn't work. http://www.womenshealthmag.com/beauty/butt-acne