I don't do buy and hold but, if I did, I wouldn't touch Twitter with a barge pole. It may be cutting edge and fashionable now, but will it be in twenty years time? The risk of the answer being 'no' is too great for my liking. Either people will tire of writing 140 character soundbites or something else will come along to knock Twitter off its perch. Or both. Besides, assuming Atilla's post about its earnings and valuations are correct, then the balance of probabilities favours a price drop rather than a price rise.
For me, buy and hold would be companies that have been around for ages and, all other things being equal, are likely to still be around in twenty years time - and doing as well as ever. Based on that most basic of requirements, Twitter doesn't doesn't even make the short list.
Tim.