SAR alerting is quite different in the US than in Canada. In the US, FSS does not alert unless you file a VFR flight plan and activate said flight plan. In Canada, if you file a flight plan, it is assumed you have activated your flight plan at the filed departure time. In the US, if you never take the flight, no problem, no one is looking for you. In Canada, there is an implied activation at the filed departure time, so you better get in touch with FIC if you got delayed or decide not to go. In the US, if you just file a VFR flight plan, but don't activate the flight plan, FSS will not generate an alert. If you file IFR, but depart VFR, no one at FSS will notice if you go missing. There are also instances if you depart VFR without a filed VFR flight plan and ATC is unable to offer the FF service at any point on your route, again no one in the FAA will initiate a search. So if you want someone to come looking for you, you need to file a VFR flight plan and activate it in the US or someone on the ground needs to know of your intentions.