They declined to reveal the location, stating they would text the information on the night.
One of the youths said it was the third party of its kind this year and the previous two had been shut down by police.
He said this one would be much bigger than the other two. Police had been told and they expected police to shut it down.
Similar parties in Rotorua in recent years have got out of control and been shut down by police. Some have provided teenagers with a shot of alcohol as part of the cover charge.
Rotorua police area commander Inspector Bruce Horne said the proposed party was illegal.
"Anyone who arranges an event of that sort would not only incur criminal liability for breaching the Sale of Liquor Act, but may also be held criminally liable should someone be harmed when attending such an event," he said.
"The general rule is that it is unlawful to supply anyone under the age of 18 with liquor. Even if a parent or guardian consents to someone being allowed to consume liquor at a private address, it is unlawful for a third party to supply someone under 18 with alcohol. In other words, liquor can only be supplied to someone under 18 by their parent or guardian."