Here is a look at notable tech companies that have conducted initial public offerings over the past two years ahead of Twitter's IPO:

FACEBOOK

The social network started by Mark Zuckerberg, which now has more than 1.1 billion users around the globe, had a rocky debut after it went public at $38 a share in May 2012, raising $16 billion in the biggest tech IPO on record.

Facebook shares fell by more than half in the ensuing months, but this year recovered to hit record highers, bolstered by strong gains in mobile ad revenues. The stock closed Friday at $49.75 giving the leading social network a market value of some $121 billion.

LINKEDIN

The social network for professionals and job-hunters, LinkedIn has been one of the biggest stars of the technology sector since turning to Wall Street in May 2011.

LinkedIn raised $353 million in its IPO, and has seen a spectacular gain in its share price, from $45 on the first day of trading to $219.90 on Friday. The market value is around $24.6 billion.

GROUPON

Online daily deals sensation Groupon went public in November 2011, raising $700 million in what at the time was the biggest initial public offering by an Internet company since Google.

But the Chicago-based company, which was listed on the Nasdaq at $20, has struggled since then and its share price closed at $9.93 on Friday. Founder Andrew Mason was fired as chief executive of the company in February amid sluggish growth. The market capitalization is some $6.6 billion.

YELP

Shares of restaurant and business review website Yelp have soared since the San Francisco-based company went public in March 2012 with a $15 initial public offering price, raising $115 million.

Yelp shares closed at $67.15 on the New York Stock Exchange on Friday, representing a market capitalization of $4.38 billion.

PANDORA

Internet radio giant Pandora Media made its Wall Street debut in June 2011, raising $235 million with stock priced at $16 a share.

Pandora, which creates personalized radio stations for users based upon their favorite artists or songs, traded below its offer price until recently but has regained ground to $25.99 on Friday, equating to a market value of $4.59 billion.

ZYNGA

Online gamemaker Zynga was valued at $7 billion when it made its play on the stock market in December 2011, raising $1 billion from investors.

But the company behind Facebook games such as FarmVille and Mafia Wars has been on a losing streak since then. Zynga shares, which were offered at $10, closed at $3.58 on Friday. Its market value is $2.88 billion.

bur-rl/rcw

FACEBOOK

LINKEDIN CORPORATION

GROUPON

ZYNGA