Social Interaction Check In Mobile App

I'm looking for a developer to help deliver a mobile app that broadly functions as follows:
- Allows users to check in to a location
- Once checked in user can see other users also checked in at the same location
- Click on other members to start chat/messaging with them

The app will be a little more complex than this with users able to create/edit/delete their account and settings, the ability to upload a profile picture when checking in to a location and choose username.

Two main features are as follows:
- subscription service as follows
- non subscription users can sign in/out a limited number of venues/locations per day and see ads in the app
- subscribed members can sign in/out of unlimited number of venues/locations per day and don't see ads
- Referral scheme where referees receive a percentage the revenue of members that they refer from the subscription and ad revenue their referred users generate

Open to suggestions about technology stack to use but would like something open source and would like this app available on iOS and Android - an open source web app version would be nice too