10/03/2009 at 07:00 PM EDT
Less than a month after amicably splitting
from wife Avril Lavigne
, Deryck Whibley hit the town in Las Vegas Friday night.
The Sum 41 singer celebrated the 20th anniversary of The Mirage where he was spotted getting close with a new woman – model/designer Hanna Beth Merjos.
Following dinner at Stack – which Whibley and Merjos entered hand-in-hand – the pair then headed to the Slash and Friends show, which featured a performance by the Guns N' Roses guitarist, as well as Tommy Lee and Daughtry.
Whibley and Merjos were later spotted getting cozy at Jet Nightclub with friends until leaving just before 3 a.m.
A rep for Whibley tells PEOPLE: "Deryck is in Las Vegas celebrating a friend's opening with a group of his close friends, including his best friend Rob Dipple and Rob's girlfriend."