How old is this rabbit?
A really young buck will not have descended testicles, so you won't be able to find them. His penis won't be very developed either; when you press just in front of it, you see a very short, round thing like a donut, with a small, round opening, that stands up the same amount all the way around. A doe's vulva is closer to the anus, there is almost no space between them at all. When you press just in front of it, it is v-shaped, with a slit for an opening. The end further away from the anus will stand up higher; it will taper down to nearly flush with the surrounding tissue near the anus.
My inclination is to say a very young buck.