I believe gospeaky is a good site to find people amd exchange your language and knowledge with them, however unfortunately you won't find a lot of Chinese there because they use websites and apps that are different than that we use.So I think if you went to the Duolingo's group for Chinese and asked there, you will find a lot. By the way, I believe you should download WeChat first in case someone asked you to use it because most of the Chinese use it. I hope i helped you and sorry for the late response. :)
I did try Tandem for language exchange with mixed results. The problem is that majority of people there are casual learners and it is difficult to find somebody reliable. But maybe you will be more successful with Chinese. You can find Tandem in App store or Google Play.