I recently returned to the USA after spending a considerable amount of time in China for business and travelling. I was able to acquire and negotiate services in four different cities: Beijing, Shanghai, Guangzhou, and Shenzen.
First, due to the 2008 Olympics the government decided to crack down on "hair salons" and other obvious prostitution services for foreigners. It is my understanding that it is much more difficult nowadays to procure services than in the past. Beijing presents many opportunities for getting some good action depending on the duration and reason for your visit. If you are staying at some 5 star hotel and have an assigned local to act as your handler/translator, I'd say go ahead and go through them versus tackling the street trade in Wanfujing and other areas. I'm sure that some hotels, and their associated massage parlors, offer discrete full service experiences. Just realize that as a foreigner, just about everything you do at the hotel or in public has the potential for being reported to someone or being tracked by someone else.
There is a lot of tail in the Wanfujing outdoor-mall area as soon as it gets dark. There are a lot of nice hotels in the area. Women of all ages and types will approach you and/or confront you depending on your game and how much of a wealthy tourist type that you look like. Try to avoid the younger ones in public because they generally don't know what the heck they are doing and can attract to much attention. Well groomed, nicely dressed, and elegant women in their late 20s or early/mid- 30's are the best bet. Most likely they will first try to take you to some "Tea House" and you'll end up paying $200 USD for a sprite, a kettle of tea, and some Macadamia nuts or Fruit Tray. You've got to be firm with them and keep the price low. This is part of the game. Generally, the street talent will not go back to your hotel until they trust you and they can shake their boss (potentially police or organized crime ring). Depending on how much cash you have, or how desperate you are, maybe you take the hit and go to a "Tea House" or "KTV" first, and then get them back to your hotel. Depending on where your hotel is, be prepared to pay for the taxi there and then give them taxi money after you're finished.
Realize that $100 USD is more than some of these women's family make in a year back on the farm or in some rural city.
Dongzhimen supposedly had a bunch of full-service massage places, but as much as I heard about it from German businessmen and young English-speaking students. For the best action anywhere in China, it's best to have some trusted colleague, or host, take you to the place that caters to the wealthy Chinese crowd. You can get Eastern European and African girls in Beijing and Guangzhou, but if you are in China...why bother with them.
Be prepared to pay exponentially more for some "internet services." I always avoided this. You don't know if it is a sting or not. But, some of the internet sites offer Chinese, Korean, Russian, Italian, African, etc. girls.
I'll finish this post at a later time. I will also post tips for Bosnia & Herzegovina, Croatia, Germany, and Israel.