I'm shy too (and incidentally grew up just outside of Plymouth, must be a west country thing!!). Despite its numerous flaws you can have success with JMB and I haven't found a better alternative.
I've used it a couple of times to set up bands with people similar to me, i.e a dads band for people with commitments but who still want to get together every few weeks to jam and gig a few times a year for fun. I actually had a really positive response, sure there were some time wasters but also some really good musicians and singers. It was pretty ease to weed out the crap from the serious.
I also once sent a enquiry to a big band who were looking for a bassist. I never got to audition stage as I worked out pretty quickly that I wasn't going to be the right guy for them (given I couldn't sight read) but it was a friendly and positive experience.
I'd say give it a try, you have nothing to lose.