Activist investor Starboard Value has built an over 9% stake in Tripadvisor after the online travel-review company eschewed takeover offers in the past year, according to people familiar with the matter.

Activist investor Starboard Value disclosed a 9% stake in Tripadvisor on Thursday and said the stock was undervalued. Shares of Tripadvisor surged 17% after the hedge fund said it purchased the shares on the belief that they "represented an attractive investment opportunity.

Tripadvisor stock soars as Starboard Value reveals a 9% stake in the global travel platform. Bernstein sees further upside in TRIP shares.