Well, many single JWs struggle with masturbation, I would expect. If they don't, maybe they stay so busy with spiritual routine that they're too tired to even think about that sort of thing. I would guess that many fall somewhere between these two extremes. Uh...or some might even live a double life, who knows?
For me, I struggled with masturbation and strong feelings of loneliness and hoping to find a wife. I didn't find anyone who seemed interested except the one person everyone thought was wrong for me. But anyone who they thought was 'right' for me either ignored me or looked at me like I'd grown a second head when I asked for their phone number.
In print, the Society does not encourage an ascetic lifestyle, but at the same time, they expect single ones to minimize time spent in entertainment, education, or work and maximize time spent studying, attending meetings, and going out in field service, apart from reaching out for great responsibilities if you're male. So...single JWs probably don't live an ascetic lifestyle unless they're very spiritual-minded.