Its obviously illegal to engage in any sort of sexual relationship with someone who has not reached the age of consent. Its also illegal in almost every state to exchange cash for specific sex acts or encounters.

Is it illegal to use seeking arrangements?

Warning About Minors: Seeking.com is for users who are 18 years of age or older. Having an arrangement with a minor is considered illegal. If you suspect a member to be underage, please ask for a photo ID, or report such members to Customer Support, and we will verify their age for you.