Cowen and Company is trimming its price target on Market Perform-rated Twitter (NYSE: TWTR) from $26 down to $17 ahead of the company's Q4 report, which is expected out after markets close today.

Analyst John Blackledge noted that sentiment around the stock has grown negative over recent user base growth concerns and its potential impact on advertising revenue growth.

Blackledge and his team are lowering longer-term estimates on Twitter, now assuming 20 to 25 percent incremental margins, versus around 30 percent prior, from FY16 - FY21. The analyst elaborated:

Our '16/'17 revenue forecast goes to $2.86 billion/$3.56 billion from $2.83 billion/$3.52 billion; for EBITDA, our forecast goes to $674MM/$871MM from $784MM/$1.08 billion, due mostly to higher R&D expense which we think will be necessary to improve the product. We introduce new 2016 quarterly estimates and extend our model to 2021. With our lower EBITDA forecasts, our long term FCF estimates also decline taking our DCF to $17. Therefore, we take our target price to $17, from prior $26, maintain Market Perform rating. We'd point out TWTR is currently trading at 7.8x '17 EV/EBITDA and <2x '17 EV/Sales, which is no longer stretched.

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