AIM 5-1-14 Closing VFR/DVFR Flight Plans
Chapter 5. Air Traffic Procedures · Section 1. Preflight
A reference copy of the official AIM text for study. It is not legal advice or an FAA interpretation; always confirm against the current official source.
A pilot is responsible for ensuring that his/her VFR or DVFR flight plan is canceled. You should close your flight plan with the nearest FSS, or if one is not available, you may request any ATC facility to relay your cancellation to the FSS.Control towers do not automatically close VFR or DVFR flight plans since they do not know if a particular VFR aircraft is on a flight plan. If you fail to report or cancel your flight plan within 1 / 2 hour after your ETA, search and rescue procedures are started.
REFERENCE-
14 CFR Section 91.153.
14 CFR Section 91.169.