In the absence of more information I think this is a question only you can answer about your service. While reading the GDPR you must consider how your service operates.
Does your service operate according to the six Principles relating to processing of personal data under Article 5?
Does your service abide by at least one of the six clauses under Article 6, Lawfulness of processing? (In the context I imagine the only possible clause is (f), that you're pursuing a "legitimate interest", if so you need to be clear about what that is.)
Does your service process the "special categories of data" under Article 9(1) and if so on what basis under 9(2)? Does your service process personal data relating to criminal convictions and offences, Article 10?
Does your service uphold the Rights of the data subject under Chapter III? Article 14 will be of particular interest.