Donal is 55 years old, 5'7'', of slim build, and wears glasses.
He was wearing a grey fleece top and dark coloured tracksuit bottoms when he was last seen.
Donal is believed to have travelled into County Donegal on the morning May 10.
The PSNI said An Garda Síochána are aware and are assisting with efforts to locate Donal.
If you believe you have seen Donal since the morning of May 10 call 101 quoting reference number 722 of 10/05/2022.