Contrary to popular belief, most arrest warrants are not actively pursued by police departments. Unless the local police department has specifically assigned a warrant team or a particular officer or detective to go out looking for him, the apprehension of the suspect will be passive, meaning that he probably won't get arrested until the police come across him randomly (for example, if he gets pulled over for a traffic violation) or if he turns himself in.
If you have any information about where he is, you should contact the police department, ask if a detective has been assigned to the case, and if so, ask to speak to that detective. Tell the detective that you have information about the suspects probably whereabouts and ask that he be arrested on the warrant.
If there is no detective assigned, simply ask to speak to an officer in charge and give that officer the same information.