Citi analyst Mark May lowered his estimates for Yelp below consensus saying the company's transition in its sales approach and recent introduction of lower-priced ad products creates near-term estimates risk. Further, Yelp's revenue growth could turn negative in Q2, May tells investors in a research note. The analyst lowered his price target for the shares to $39 from $40 and keeps a Neutral rating on Yelp. On the positive, however, the stock's valuation is low and near trough levels, says May. Moreover, recent activism could be a positive catalyst, including a potential acquisition or other operational improvements, the analyst writes.