At this summer's HOPE conference, Joshua Aaron spoke about ICEBlock, his iPhone app that allows users to anonymously report ICE sightings within a 5 mile radius, and to get notifications when others report ICE sightings near them. You can see the full talk, and the lively/infuriating Q&A, here,
No, the thing that’s lost is all the vulnerable people using an app filled with vulnerabilities waiting to be exploited by a vindictive government.
If you actually read the post they go into detail about this.