Underage drinking.
I am an underage drinker. I will admit that right now with no shame. I happily break the law every other weekend. Who is the victim in that? Nobody except myself. But then, I'm choosing to drink. The risks that drinking entails, I am bringing them upon myself. Yet, I could get a criminal record or a fine or both for risking damage to my own body and my body ALONE. With that kind of attitude they may as well outlaw self-harm, extreme sports, etc. You could say that there is potential victims of underage drinking, such as people around the underager... however... if I was to drink, get violent and hit someone, that'd be assault. It may or may not have been caused by the drink. If I was 18, I'd probably have done it anyway if I was that kind of drunk. So there's no victim to underage drinking.
Underage smoking too.
People in the general area of the underage smoker could be passively smoking, but they would be anyway if the smoker was 8, 18 or 80. The age of the smoker doesn't change any effects their smoking has on people around them. So there is no victim to underage smoking.
Drugs do not directly have any victims. Obviously there's the gangs and murder associated with the sale of drugs, but the actual act of consuming that drug has no victim.
Sex. CONSENSUAL underage sex has no victim. If two underagers know what they're doing and they're aware of the risks and the measures they need to take to reduce them, leave them be.
Loitering. OH GOD FORBID WE STAND SOMEWHERE. I've noticed that it's mostly teenagers that get into shit for this because people (generally the elderly) like to assume that anything aged 16 is out to mug them, rob their house or stamp on their garden.
I could probably list more...