Should men that hire young women who are forced to be prostitutes against their will be punished more severely in order to deter them from getting involved in the exploitation of these vulnerable young women?
Ideally, such men should be punished more harshly, but in practice, they cannot and should not be. The reason for this is that it would be exceedingly hard to expect men to know why a given woman is acting as a prostitute.
Let us think about how men could possibly find out if a prostitute was working in the sex trade of her own free will. The most likely way would be for him to ask her. The problem is that she would most likely lie about it. A woman forced into prostitution is typically going to fear the people who have forced her into that life. If she wanted to get away, she could probably go to the police or to some aid organization and ask to be protected. Clearly, if she is still working, she is doing so because she is intimidated. She will therefore not tell the man that she is unwilling. If she is in a brothel, she might not be able to get away, but she is still likely to be afraid of what will happen to her.
Thus, there is no practical way for a man to know what motivates a prostitute that he hires. This law would probably not work to reduce the incidence of men patronizing unwilling teen prostitutes.