The number of people browsing online dating sites for a sweetheart has dropped by nearly a third, as the once explosive market slows, a market research firm said Wednesday.

Revenues from dating sites are expected to increase by only 9 percent this year to $516 million, according to JupiterResearch, a division of Jupitermedia Corp. The growth rate has dropped dramatically since 2002, when the industry grew 73 percent. In 2003, it increased by 77 percent, but dropped to 19 percent in 2004.

Contributing to the slowdown is the fact that the online personals market is maturing, JupiterResearch analyst David Card said. Young markets, which have a small customer base, show high growth in the early years, and then slow as the number of customers increase.

Before the Internet, personal ads were mostly found in alternative newspapers. But once they moved to the web, then the market took off.

"It was a social and technology phenomenon," Card said. "The two of them came together at the same time."

But it appears the love affair is fading.

Based on a survey of more than 2,300 online adults, 33 percent fewer consumers are browsing online personals today than a year ago, JupiterResearch said. In order to generate more revenue from fewer potential customers, dating site owners need to focus on "serious daters," people looking for long-term relationships or marriage.

Serious daters convert 20 percent more often than casual daters to paying subscribers, they are twice as likely to buy long-term subscriptions, and they pay up to twice as much per month, JupiterResearch said.

The survey found that 44 percent of adults using dating sites were looking for a serious relationship, 43 percent for friendship, 39 percent for a date, 37 percent for physical intimacy and 20 percent for marriage.