11:33 AM PT -- The NBPD just released a statement on the Josh Giddey investigation ... saying officials are actively seeking more information and pursuing all leads and evidence to get the facts of the case.

NBPD says the investigation remains active ... and is working to conduct a "fair and thorough" process.

The inquiry into whether Oklahoma City Thunder guard Josh Giddey had an inappropriate relationship with a minor has hit a roadblock -- TMZ Sports has learned the alleged teen and her family are refusing to cooperate with officials.

Law enforcement sources tell us police would obviously like to speak with the purported female and those close to her to gather more information regarding the social media claims that made rounds over the weekend ... but as of right now, no one is talking.

It's a significant component to the whole situation ... as a lack of cooperation will make it much more challenging for officials to determine whether any laws were broken.

As we previously reported, Giddey is being accused of having an intimate relationship with an underage girl from California ... with photos and videos allegedly depicting them together.

The NBA is "looking into" the matter ... but Giddey has continued to play for the Thunder following the bombshell allegations.

The 21-year-old was asked about the claims at practice on Friday ... but elected not to speak on it.

Thunder coach Mark Daigneault also shot down a question regarding the inquiry prior to Tuesday night's game against the Minnesota Timberwolves ... saying he would not discuss anything off-court related in reference to Giddey, and he will continue to play.

Giddey played 28 minutes and scored 10 points in the loss to the Wolves ... and fans at the Target Center showed their disproval by booing him relentlessly throughout the contest.