When professional networking site LinkedIn debuted on the NYSE in May, shares opened at $83, double the initial offer price.The first high-profile tech firm to go after an IPO in months, LinkedIn signaled a turning point for the sector. Shares of LinkedIn have cooled since then, closing Friday at $63.08. Earlier in November, LinkedIn completed a secondary offering, raising $88 million and doubling the number of shares available in the public markets. The selling shareholders included Bain Capital which sold all of its 3.7 million shares, around 4.2% of the company. During the most recent quarter ended in September, LinkedIn said its membership base grew to 131.2 million, an increase of 63% from the same period last year. The company reported its first quarterly loss since going public, while revenue more than doubled to $139.5 million, sparking concern that the company is overspending. Analysts believe much of LinkedIn's growth will come from new products, particularly as the company opens up its platform to third-party application providers. In April, LinkedIn announced it was releasing plug-ins that developers could integrate with their own Web sites which allows users to share articles with the LinkedIn community, view member profiles and browse company data. "To sustain robust revenue growth rates, the company will need to have to move beyond simple hiring solutions and enter new markets," Morningstar analyst Rick Summer wrote in an analyst note.