Here is an easy link to a map of the Sylmar area ...
http://www.zipareacode.net/sylmar-ca.htm
If you zoom in one level, you will see the community names previously mentioned (southwest of Sylmar). You can zoom in more ... even to a satellite view where you can see the streets. I can see a McDonald's hamburger joint on the northeast block of Encinitas and Roxford.
(McDonald's 12860 Encinitas Ave, Sylmar, CA 91342)
which is right across the street from the where the volunteers met for the canvas
(Denny's 12861 Encinitas Avenue at Roxford Street)
Here is a link to cell phone towers for the various carriers ...
AT&T, NEXTEL, SPRINT, T-MOBILE, VERIZON
... although we don't know which one Gavin used. There are a lot of towers, so the area where his phone stopped working should be precise ...
http://www.cellreception.com/towers/towers.php?city=sylmar&state_abr=ca
By now his family should have received his phone bill which would detail
all the phone calls he had on the night he went missing.
If someone took Gavin's car to a chop shop, then they may have had an accomplice for transportation home ???
Recently on the Headline News channel, I saw how LE caught the murderer of a young woman who went missing while bicycling home. He was traced because LE collected local surveillance footage of the vehicle (and license plate) that followed her. So I hope they are using that strategy for Gavin.