Air taxi pilot reported responding to a TCAS RA during approach to HWD which was caused by an aircraft flying near the final approach area and not in communication with ATC. Air taxi flight crew was vectored back for approach and landed.

Narrative

On descent into HWD; I was the pilot flying with the autopilot on. Approach control had just cleared us for the RNAV 28L. Approach was armed and localizer and glideslope captured. Shortly after ATC advised us of traffic ahead and to our left below us. It was a VFR target and they weren't talking to them. We looked visually and didn't see them. The TCAS gave us a traffic alert. ATC then told us to cancel approach and climb back up to initially 3;400 and then to 4;000. Shortly after the TCAS gave us a RA of monitor vertical speed. Since we were still descending on the approach; I disconnected autopilot and leveled us off and then started to climb back up. We told ATC responding to an RA and need to be resequenced for the approach. Shortly after the TCAS announced clear of conflict. We circled around another approach and landed normally with no further issues. Cause: Unaware VFR traffic not in communication with ATC and turned into final approach area. Suggestions: Perhaps ask ATC for vectors away from traffic earlier before it became a TCAS event.