I understand that neopets is not a personal site however, the link that you are providing is a referral link which means that if other members use it to sign up to Neopets then you gain NP as a reward. This is considered to be personal gain. Advertising of websites where personal gain is derived is also banned here.
If you wish to tell people about Neopets.. that is great! You are quite welcome to as long as you don't use a referral link.