Yes, think of it, it's common sense that they have too; The stems carry all the THC to the buds, leaves, seeds, etc. So there's however much THC in the stems as there was when they were picked and stopped transporting THC. There also can be quite noticeable (well on good stems..) amounts of crystals on the outside of the stems. You can use them in the making of cannabutter... like last time we made brownies, a friend had like what looked like a quarter of bud as far as how much it filled up the bag, but it was actually just juicy stems... put it in a sock, put the sock in the butter, and awhile later, we had cannabutter.
I've never been told if there's something different about the THC in stems and it just doesn't come out in smoke, or that there's just not enough of it by the time you burn the stem to effect you... but you could throw them in some vodka, let the alcohol absorb the THC, and awhile later, drink up