He has a $30 price target.
Here's his explanation:
BOTTOM LINE: We are downgrading our rating on Twitter to SELL as opening trading levels on Twitter fall well above a 15% range above our price target of $30 (modified from $29 previously to account for additional cash raised at the final $26 IPO price vs. the previously indicated $25 level). At a price in the high 20s or low 30s (which seems to us a reasonable price range) and based on our best assessment of Twitter's growth prospects and appropriate drivers of our discounted cashflow valuation (all determined on a basis that is relative to the variables we use to value Google and Facebook), Twitter would be fairly valued. However, with a price that pushes into the high 30s and beyond, Twitter is simply too expensive. At a $45 price level (the stock opened at $45.10), the enterprise value is approximately $30bn...or almost the same valuation as Discovery Communications, and nearly the same valuation as CBS or the combined Publicis Omnicom Group...or even Yahoo (some will argue that Yahoo's stake in Alibaba is worth this much, too).
Put another way, our price target equates to a 2018 EV/FCF multiple (which we think is an apt comparison, because by that point in time the business should be relatively mature, if still faster growing than peers) of 21x, vs. Facebook at 17x and Google and 16x. At $45, Twitter would be worth 32x. We do note that one way to justify a $45 price in our model would involve presuming that Twitter could generate more than $6bn in annual revenue by 2018. However, we think that would seem overly optimistic to us given our best assessment of the industry and the business at this point in time.