Demi Lovato is on a House Party Tour

Demi Lovato is on a mini tour to promote her new song which includes house parties featuring local celebs. She kicked off in Boston with Rob Gronkowski.

Demi hosted a rager Tuesday at a pad she rented in Beantown, which was stop #1 in her "Sorry Not Sorry" House Party Tour ... which is exactly what it sounds like.

Sources close to the singer says she came up with the idea at a recent house party ... wanting to offer fans an intimate setting to enjoy her new single, "Sorry Not Sorry." As for how Rob got involved ... we're told she wanted to invite a hometown hero ... and he happily obliged.

Demi hosted about 200 guests from the area, and ended up doing 3 songs, including "Sorry Not Sorry".

The Boston #SNSHouseParty was out of control!!! Thanks for rolling in with me like a champ @Gronk □ @kiss108

A post shared by Demi Lovato (@ddlovato) on Jul 11, 2017 at 8:31pm PDT