He came across his old friend while walking in the park.

He dropped in on some old friends during his vacation trip to New York.

He met one of his old friends on his way back from the station.

I ran into an old friend at Tokyo Station.

Walking along the street, I happened to meet my old friend.

Walking along the street, I met an old friend of mine.

I ran across an old friend in the street.

The other day I met an old friend on the street.

I met an old friend of mine the other day.

The other day I saw an old friend of mine.

At Narita Airport, I ran into an old friend of mine.

I ran across an old friend in the street.

I ran across an old friend of mine at party the other day.

I met an old friend by chance at that party the other day.

I caught sight of an old friend of mine in the crowd.

Yesterday I ran across an old friend of mine at the airport.

I unexpectedly met an old friend of mine on the bus yesterday.

I ran across an old friend of mine at the party yesterday.

As I got the train this morning, I met an old friend of mine.

I still correspond with an old friend of mine from time to time.