Have you tried Makaton?
DS actually started to talk when
He was 2 and a half, but this was a very sloooooooow development and at 4 his saying his 10 words.
DS has his own made-up sign language that he uses to mainly communicate with me. Being a bit "dumb" I should say at the time. When he used his gestures, I
Didn't say the word or used the same action. I just did what he asked. When I started doing that more, he became more verbal.
So I thought 'light bulb moment' Makaton would be really useful and he uses the words with them.
I've never tried PECS, but you can try Makaton.
Also DS uses a lot of exclamatory words. i.e. "Uh-oooooh", "woooops", "yuuuck" "gasp" etc. I think you should incorporate these into your play and daily routine. For example, if you see something yucky on the floor, point to it (if your child can follow a point) or show your child the yucky thing and say "eeeeew, yuk". When your pulling something do a strained voice.
I got these ideas from the www.teachmetotalk.com site, she is sooooo good. I recommend you look at this site.