Here are some sites/casinos that accept PlayPlus prepaid cards:
888 Sport NJ
Mohegan Sun Casino
How PLAYPLUS works?
PlayPlus allows customers to load their prepaid Play+ cards with their credit or debit cards, and then forward that money on to their online gaming accounts. You can get a Play+ prepaid card in the mail that can be used to access your funds instantly via ATM and to shop anywhere Discover is accepted.
If betting is legal in your state, PlayPlus can be used at most sites. In Alaska, Idaho, Minnesota, and Wyoming, the age to gamble is 18. Everywhere else, the age is 21.