Take the loss. you still have a profit anyways overall. you win some, you lose some. (holding onto a losing trade because you think it will turnaround...an amateur trader thing to do.)
That suggests that it's not one you'd choose to buy, at its current price, under other circumstances and with plenty of available funds? But surely that's effectively what you'll be doing, if you keep it rather than selling it? I don't know and understand enough about your situation to be able to answer this question confidently, but from what you've said above, all my instincts are that I would sell. I look at it the other way round from you, I think: if I wouldn't want to buy the stock at its current price, why would I want to retain it rather than selling it?
From sprsptd... "... suppose you don't take the loss this year and your portfolio is flat the next year - well then you'd only be able to take $3,000 of that loss in 2016 (and have to defer the rest). So take the loss - it is a no-brainer. You get to take the full amount of the loss this year and you save on your taxes..."
The time value of money is nothing, since interest rates are zero, so it doesn't really matter what year you realize a loss. Some slow learners still think in terms of 5%ish interest rates from years back.
It matters a great deal if he doesn't have trader status with the IRS, and it matters almost as much regardless. I'd take the loss against his gains now were I him. The present is always more certain than the future.
What are the reasons for NOT booking a loss this year? If his only reason is because he "hopes" twitter will take off, that's a horrible strategy, IMO. I feel like you can't go wrong booking a loss as early as possible for in a taxable account. Always reduce your current taxes whenever possible.
So OP has less than 24 hours to make a decision and he hasn't responded once. This is a troll thread.