A recent boyfriend of missing Cornwall woman Kirsty Noden is understood to have been arrested on suspicion of murder.
Miss Noden, 32, has not been seen by neighbours in Marazion, near Penzance, since January.
Her social media accounts have also not been used over the same period, Devon and Cornwall Police said.
A 22-year-old man from Marazion, who is understood to be Miss Noden’s most recent partner, has been arrested and is currently in custody.
Detectives would like to hear from anyone who believes they have seen or heard from Miss Noden more recently than January.
She has links to Torquay, Ellesmere Port, Crewe and Merseyside.
An investigation was launched after police were contacted by another force expressing concern for her welfare.
Detective Inspector Ben Beckerleg, who is leading the investigation, said: “We are pursuing a number of lines of inquiry.
“We’re keen to hear from anyone who believes they have seen or had contact with Kirsty since January.
“It is possible Kirsty has gone somewhere and for reasons not yet clear, does not wish to be found.
“We have arrested this man, who we understand to be Kirsty’s most recent partner, in order to speak to him formally and obtain his account of events.
“We are urging anyone with information, no matter how small, to contact us as soon as possible.
“Even a small detail could prove critical in this investigation.”
Miss Noden is described as white, of heavy build and 5ft 8in. She speaks with a northern accent.