Smiles - sorry this is a year late! The park is Dongdan Park about 3 blocks east of Tiananmen Square and then turn south. It's a smallish park right there almost at the intersection.
As for the comment in the OP, I have written several times both here and in gaythailand about the dangers of picking anyone up off the street in China. It is not just AYOR. It is downright dangerous. Millions of guys from the countryside flood into China's main cities in the hope of finding work. Many end up with casual day jobs. Others are less lucky. Scamming tourists has become one way to make a living, and scamming gay tourists to make a better living! That cute guy who offers a massage in your hotel room or a couple of hours of sexual delight will almost certainly be rent of some description, and dangerous rent at that. Once at the so-called massage parlous or even your hotel room, you are at great risk of some of the guy's friends turning up and threatening you in all manner of ways. I made my mistake and was lucky I was in a 5-star hotel with very good security and got away very lightly. I've been back in China dozens of times since then, love my trips and I've enjoyed some fantastic times with quite a few great guys. But no-one should ever - EVER - trust anyone they happen to bump into on the street in China. Why the person mentioned in the OP did not do just a little more research re a country he had not visited before totally beats me!