Facebook paid 16B Dollars for 400,000,000 active phone numbers and all the personal info bound to them. It's not the app itself it's the data, you know it well too.
There were some recent papers on algorithms how to do it, and they managed to match ~90% of 'anonymous phone numbers based on the facebook graph data. You stay anonymous only if all your friends and their friends care about anonymity as well.
/s