Can the police get a warrant if someone told them I was doing something illegal?
No, that probably is not enough to get a warrant. However, if law enforcement receives a tip or information that you are engaged in criminal activity, then that can begin an investigation. During the course of that investigation, if law enforcement independently witnesses additional evidence in support of a warrant, then law enforcement can petition the court for the purpose of obtaining a warrant. The answer to the question is, by itself no, but it could be the beginning of an investigation that ultimately gives law enforcement the authority to obtain a warrant.