'Mob Wives' Star Natalie DiDonato Currently Missing ... After No-Show for 2 Flights Home

"Mob Wives" star Natalie DiDonato is the subject of a missing-persons report ... after we're told she was MIA for 2 separate flights home.

Law enforcement tells TMZ ... a report was filed for Natalie -- best known for appearing on season 5 of "Mob Wives" -- this morning in Las Vegas and it's currently being investigated.

We're told Natalie's family is concerned, and her whereabouts are unknown -- they spoke with cops in Philadelphia, where ND reportedly visited earlier this month ... before missing a January 5 flight home to Florida.

We spoke with Natalie's mother, Denise Fuoco, who tells TMZ ... she last spoke with Natalie 7 days ago, when she got her on a FaceTime call.

Denise says they had a brief conversation, but Natalie rushed off the phone and didn't clarify where she was -- just telling her she had to go.

Natalie's mother says it's unclear if her daughter was with anyone during the FaceTime call ... but notes the reality TV star looked nervous and distressed during their brief chat.

Denise tells us the conversation left her concerned -- she says she tried to call her daughter back on both of Natalie's cell phones ... but claims neither was working at the time.

Denise tells us she repeatedly tried to get in contact with Natalie over the next few days, but failed to reach her ... prompting her to contact police in Philly.

According to Denise, the last update she received was from one of Natalie's friends, named Ben ... who allegedly told DF on Monday the "Mob Wives" star was now in Las Vegas and had reached out to him for help getting back home to Florida.

Denise says Ben claimed Natalie contacted him 4 days earlier on WhatsApp, where she sounded distressed and asked for money for a flight.

Denise says Ben purchased a ticket for Natalie ... but she never made the flight to Florida.

This friend is believed to be the last known person to have spoken with Natalie ... and he was the one to file a missing-person report in Vegas.

Denise says Natalie hasn't been right for the past month ... but isn't sure what's going on with her daughter -- noting the TV personality has been "distant."

Understandably, Denise tells us she's "sick" over the situation and is struggling to sleep during the ordeal.