A Victorian teenager who groped several woman in the surf at a Gold Coast beach has avoided conviction.

The boy, who was born overseas and whose actual age is unknown due to a lack of records, pleaded guilty to nine counts of sexual assault and three counts of common assault at a Children's Court hearing at Southport on Wednesday.

He has been placed on a two-year probation order for what Judge David Kent described as "serious" offences.

The court heard the boy touched eight women aged between 15 and 24 in the surf at Surfers Paradise beach on January 12, 2016.

Prosecutor Nicholas McGhee told the court the assaults variously included the boy touching his victims' buttocks, vaginas and breasts, sometimes under their bikinis.

Mr McGhee said after raising the alarm with a local lifeguard, several of the women identified the boy in the water swimming behind other complainants in "quite a predatory manner".

"People should enjoy the right to enjoy the right to have fun at the beach without being sexually assaulted or assaulted by a stranger," Mr McGhee said.

Judge Kent ordered the boy to undergo a "positive sexuality" course as part of his probation and said while his immersion in a new culture partially explained his actions, it didn't absolve him.

"This is obviously unacceptable behaviour but it is also criminal behaviour," he said.

"Your behaviour had significant impact on at least two of the complainants.

"The impacts on them have been considerable."