Media reports said Simon Cheng, who is thought to be from Hong Kong, is believed to have gone missing on August 8, the BBC reported.
The Foreign and Commonwealth Office (FCO) said that it was "seeking further information from authorities in Guangdong province and Hong Kong".
"We are concerned by reports that a member of our team has been detained while returning to Hong Kong from Shenzhen," an FCO spokesman said.
The British embassy in Beijing is providing support to the family, he added.
In its report, the Hong Kong Free Press newspaper said that Cheng was a trade and investment officer at the Scottish Development International section of the consulate, and had travelled to a business event in Shenzhen on August 8 via the Lo Wu immigration control point.
His girlfriend told news site HK01 he had planned to travel home by train the same day, but did not return.
Travellers have described heightened security measures at the border between Hong Kong and China, as Beijing looks to curb anti-government protests in Hong Kong, the BBC reported.
Recent travellers have reported that everyone passing through the border from Hong Kong into China was subject to police checks on the mainland side, where officers took people's phones and scrutinised their photos and videos.
The protests, now entering their third month, were sparked by the now-shelved extradition billl, which would would have allowed criminal suspects to be sent to mainland China.
It has now grown into a broader movement calling for democratic reform in Hong Kong, and an investigation into alleged police brutality against protesters.
( With inputs from IANS )