To be honest, I'm not a fan of consultants until you know where the problem lies. What do you want them to achieve? Having an idea of what the specific problem is will give you more control, and more chance of them achieving your goal. (I get most my income doing consulting, albeit not in the social media sphere!)
Most important, know what you're wanting to achieve via social media; is that simply more traffic, or engaging with existing customers and dealing with after sales support?
If you're trying to generate buzz and have existing customers, give incentives to them to send invites, or post about you. Perhaps a free month of premium service for all users who a) 'Like' and b) post a review on your Facebook page. Or the best 10 get 20% off next order. Only you know the sort of incentives you're able to offer and may work with your customer base.
Remember to strike a balance here - you're trying to get happy customers to help get you referrals, not browbeat them via email until they are unhappy customers!
Do all you can to make it easy for your customers to join in.
Be responsive and react to comments about your service/products. It's likely to be somewhat time consuming though. Good luck!