Michael Phuong Minh Nguyen disappeared on July 6 amid large-scale protests in the country.
Convicted of disrupting public order, most are handed prison terms of from eight months to over a year.
The move follows a visit by a US embassy representative, an activist network says.
Nguyen Ngoc Nhu Quynh's mother has had no word of her since July 18, she says.
The rights group says Vietnam’s record has worsened, despite promises it made at its last UN review.
Will Nguyen had joined mass protests over a land concession proposal for foreign companies.
Will Nguyen was beaten and detained during a protest over a long-term lease scheme for foreign firms.
Nguyen Hai Long, a resident of the Czech Republic, says he helped Vietnamese secret police grab Trinh Xuan Thanh, now serving two life terms in Vietnam.
The three-month suspension doesn't affect the paper's print version, however.
They say the exchange of information fostered by the firms is at risk amid a clampdown in the country.
William Nguyen's sister says she is 'prepared for the worst.'
Nguyen Ngoc Nhu Huynh is in poor health and 'getting thinner,' her mother says.
Meanwhile, in a separate case, an anti-corruption blogger is sent back to prison after a court rejects his appeal.
The men were handed lengthy sentences in January for producing videos critical of the government.
Meanwhile, Thai police cancel the showing of a film documenting the hardships of her family's daily life.
Failures by police to respond point to likely government complicity in the attacks, rights groups say.
Another activist is meanwhile transferred to another prison with no word given to his family.
Villager Bui Huu Tuan self-immolates following an unfavorable court decision on his complaint against authorities.