I agree with SoCalBoston also...
I would also suggest when you meet people on walks, ask them to
completely ignore him. No talking or eye contact. Just calmly carry on their conversation with you. You might even had them a treat and ask them to nonchalantly drop the treat to him, still not looking or talking to him.
If he seems ok, they could squat down, still not looking or talking, and if he feels comfortable he can sniff the person without feeling threatened or overwhelmed... Ask them not to pet him, just squat...
Hopefully over time he'll feel more comfortable around strangers...
