Haad Rin is the most famous and developed beach on Koh Phangan, this is where the famous full moon party takes place every month. There are many nice beach bars and clubs, and if you walk around in the streets behind the beach, you can find some more bars and massage salons.
Important: There are no such girly bars or beer bars in that area, but a few massage salons with girls who will give you a hand job for a small tip. Which I assume you are. The good news is that there are many nice beach bars on Haad Rin with cheap drink prices all night long see below. It will be more fun if you meet a girl in one of the beer bars see above and then take her to a bar on the beach to have a relaxed drink together.
They have fire shows going on each night from about 8pm. Mellow Mountain Bar is a nice open air disco on top of a hill overlooking the beach, but it only gets busy during the full moon party.
And if you walk around in the town of Haad Rin, you will find several more bars β they all look really nice, but again the problem is that there are no Thai girls. The full moon party is probably the most overrated tourist event in Thailand. I imagined getting a free blow job in a dark spot on the beach and walking back to my hotel hand in hand with two hot Thai girls.
To make it short: Different location, same crowd. The massage salons are, along with the girly bars, the two best places to meet Thai girls on Koh Phangan. I have marked the main clusters of massage salons on the map below. Most of them are working in the girly bars near Thong Sala and in the massage salons of Haad Rin. Yes, they are working together with the girls so you will need to be able to tell the difference between girls and ladyboys like on my photo above, the ladyboy there is the one in the white shirt.
