Can't say I've been to the half moons, but I went to two full moons in Koh Phangnan (Had Rin, Thailand). First off, if you haven't left Had Rin, leave now. It's gross and seedy and if you wake up there after a party...well just leave now. Take a long boat (don't pay more than 90 baht) and go to Had Yuan (like 5-10 mins upshore). Stay at Big Blue. It's beautiful, pristine, there's a b-ball court, food and staff are great, rooms are cheap. Longboats don't run at night, but you won't leave until 5-6 in the morning anyways.
As for drugs...be careful. Don't trust anyone...even 'ferengs'. Cops are galore and they likely won't arrest you, but they will take everything in your bank account.
PM me if you want more help.