Hello Sally. I have no experience of catching stray bunnies but you could try a humane rabbit trap? You might be able to borrow one from a local wildlife sanctuary or the PDSA? In fact, I'd be inclined to ring the PDSA or RSPCA and ask for their advice. And try not to worry, if he's been out for more than a week then he's obviously got a survival instinct. I assume you've already put up 'found' notices on lampposts etc?
G x