The service is parting with Surname & Surname, which will not repitch for the account, after 16 months and has shortlisted a number of agencies.
The pitch comes as the app holds the top spot for overall cab app use in London, despite reportedly being the last to market of eight taxi-finding apps when it launched in the capital two years ago.
Sara Holt joined Hailo as head of marketing in April, having worked at Global Radio for three years.
Calling the service 'by far London's number one taxi app', Holt said: 'We can confirm that we are reviewing our UK consumer PR arrangements as we plan for further success. The process is under way and we have a shortlist in place. We will announce our new PR partner in due course.'
The company has about 200 employees and annual sales of $100m (£65m).
In London, it has signed up 13,000 of the city's 20,000 black-cab drivers to the service. Since launching, Hailo has branched out into nine other cities including New York and Madrid, and is targeting Tokyo next.