Finding someone that ONLY speaks English would be your best bet, if you are around someone who speaks Mandarin and English then of course you would go to your native language. So make a friend that speaks English only and then you'll end up being forced to speak it. :)

Many language students are reluctant to engage in a conversation because, on the one hand, they do not wish to make mistakes in front of others, and, on the other hand, want to avoid the stress that comes with having to think quickly in a foreign language. If the student is speaking with a close friend there is less likelihood of feeling embarrassed. So, the solution to your problem might be to first find a foreigner learning your language, one with interests similar to yours, and establish a friendship. I think then there would be less pressure on you. 许多学英语的学生不要跟英语为母语的人交谈因为,一方面他们不要说错, 另一方面是, 面对面地和外国人讲话的时候, 他们不能快快得想起来怎么讲英语，因此要避免 压力和紧张。 如果 那位学生跟一个好朋友讲话，那么容易得多。大概不会感觉困窘的。 所以也许问题解答的是首先寻找一位学你的母语的外国人， 一位跟相同的兴趣的人，交朋友。 那样开口的压力小得多。

Here are 5 tips for overcoming your shyness http://www.italki.com/knowledge/page/How%20to%20overcome%20shyness%20in%20making%20conversation.htm

Believe me , this situation is very common among non speaking English person. 90 % people shy to speak. Even myself also was a weak point for the same problem. But the easiest way is to speak secretly with little children, they won't laugh on you even you speak wrong.

It's totally Okay to speak out loud,I bet you must know the Crazy English Li Yang,let's firstly set aside his study methods,but his study spirit is really worthy learning.You know,it doesn't matter what you speak,but that you can speak something out really matters.Just imagine yourself alone,no surrounding people,don't need to be afraid of other people's opinions.Just try to speak it out,then your English can be improved a lot