With technology stocks in the U.S. hitting another record this month, Japan's equivalent of the FANG group (Facebook, Amazon, Netflix and Google) may appear too cheap to ignore. Don't be so sure.

Shares of the three largest internet firms have pretty much collapsed. Portal operator Yahoo Japan Corp. and e-commerce company Rakuten Inc. have tumbled more than 25 percent this year, while instant-messaging service Line Corp. has lost about 11 percent.

Their performance is drawing bets that the worst is over. Eashwar Krishnan of Tybourne Capital Management sees a 125 percent upside for Line shares, citing the trajectory followed by Facebook Inc. and Tencent Holdings Ltd. Line hasn't even started making money from its 170 million monthly active users yet, Krishnan said at the Sohn Hong Kong investment conference last month. Line earns 0.12 cents per user minute spent, versus Facebook's 0.75 cents.