The three, two men and a woman, had left the festival area in Tantolunden park when they were attacked by two skinheads, who were in their 20s.
The assault was said to have been motivated by homophobia.
On Friday morning the attackers were still at large, but witnesses were able to give police good descriptions of the men.
The Pride festival, which targets the gay, bisexual and transgender community, has attracted thousands of visitors to its week-long programme of performances, workshops and debates. On Saturday there is a parade through Stockholm, and the festival closes on Sunday with a party in Pride Park.