Yelp Inc. (YELP) shares have lost 20.7% in the year-to-date period, underperforming the Zacks Computer Technology sector, Zacks Internet Content industry and the S&P 500’s return of 30%, 14.8% and 26.1%, respectively.Given Yelp’s position as the leading source of reviews and ratings for local businesses, this underperformance is disappointing. This raises a crucial question for investors: Is it the right time to buy, hold or sell Yelp stock?Yelp Faces Competitive and Economic HeadwindsYelp’s Restaurant, Ret ...