Christie has stops scheduled in Georgia, South Carolina and North Carolina on Tuesday.
The fundraising swing continues Wednesday.
Christie has helped Romney raise $2.1 million in two New Jersey fundraisers. The pair pulled in $1.7 million in June and $400,000 during a prior event when Romney was still being challenged for the GOP nomination.
Christie has fueled speculation that he's being considered for vice president. But he's also indicated that he considers himself too blunt-spoken to be a likely choice for the presumptive GOP nominee.
Romney will be in western Pa. on Tuesday, before leaving next week to visit the Summer Olympics in London.