The Electoral Commission says a quarter of younger voters still have not enrolled to take part in this year's general election.
Almost 36,000 people enrolled to vote or updated their details on the electoral roll since the Prime Minister announced the election date.
Across all age groups 92% have enrolled, but among 18- to 24-year-olds just 75% have done so.
Polling will take place on Saturday 8 November, and eligible voters can enrol until the day before then.
The Electoral Commission's chief executive, Helena Catt, says social networking sites are being used to encourage young people to enrol.
She says the aim is to have 95% of all eligible voters enrolled by election day.