Written by StockNews.com

Prominent digital marketing firm eMarketer lowered its 2017 revenue outlook for Snap Inc. (NYSE: SNAP) by $30 million on Tuesday, to $770 million, citing higher than expected revenue sharing with the company’s ad partners…With advertising representing nearly all of Snap’s revenue, any hiccup on that front is major bad news.

As Reuters reports, the forecast is much worse for fellow social media giant Twitter Inc. (NYSE: TWTR):

On the other end of the spectrum, eMarketer forecasts more trouble for Twitter Inc., which has been grappling with stagnant user growth. Its U.S. ad revenue will decline by 4.7 percent to $1.3 billion, and Twitter’s market share of the U.S. digital ad market is expected to drop to 1.6 percent in 2017 from 1.9 percent last year.

Since its much anticipated IPO last month, Snap’s stock has see-sawed amid a general downtrend. The stock hit a high above $27 soon after its initial public offering, but its second week of trading turned decidedly bearish, and SNAP now sits around $21 per share.

Snap Inc. shares fell $0.38 (-1.85%) in premarket trading Wednesday. Year-to-date, SNAP has declined -15.93%, versus a 5.98% rise in the benchmark S&P 500 index during the same period.