Urgent UX/UI Designer Needed for Web and Mobile App

I'm looking for a UX/UI designer who can upgrade some areas of design to enhance the user engagement. .

Key requirements include:
- Design experience specifically for both web and mobile platforms (app)
- Proven track record of increasing user engagement through UX/UI design
- Understanding to capture professional audience
- Ability to work on an urgent time frame
- Share your portfolio

NOTE: I need the best designer so I'll check almost every bid.